2 Degrees and Extreme Weather

Welcome back to our investigation into 2 degrees of warming and how this might affect the habitability of regions of Earth! So far we've covered how temperature and sea level rise under the 2 degrees scenario could make it difficult for humans to live in affected regions. There are of course many other different impacts so I'll be writing a few, but more brief, posts to explore this.

Today I'm looking at extreme weather. This includes more intense and more frequent storms, extreme conditions such as El Niño and La Niña years (see my other blog for more depth), heatwaves, and other extreme events.

If we cross the 2°C of warming threshold, and indeed if we continue to see a rise in average global temperature (even if it is 1.9999°C at its peak), it is generally agreed that extreme weather events will become more frequent, and more intense. The IPCC Fifth Assessment Report explains that climate change related risks from extreme events, such as heatwaves, are already moderate with 1°C of warming and there is a high likelihood that this risk will increase as temperature does. In a specific FAQ, they go on to explain that changes in the frequency and intensity of extreme events are likely to occur, even with small mean climate changes. Here's a quick breakdown (by order of most likely):

Heatwaves:
- Increased risk of more intense, more frequent and longer-lasting heatwaves
- Likely to have a decrease in the daily range of temperatures in most regions
- Likely to have fewer frost days (temperatures below freezing), and thus longer growing seasons
- However exceptions could occur due to changes in atmospheric circulation, most likely in regions such as western North America

Christidis et al. (2014) focus on the European heat wave of 2003, where tens of thousands of people died, and the likelihood of severe heatwaves in the future. According to them, an earlier study suggested that human influence "at least doubled the chances" of the event, and forecast that severe heatwaves could become commonplace by 2040. This newer study found that extreme events that would occur twice a century in the early 2000s are now expected to occur twice a decade.

Heat wave duration index from the Warming World: Impacts By Degree booklet, based on the National Research Council report Climate Stabilization Targets: Emissions, Concentrations, and Impacts Over Decades to Millennia (2011)

Fischer and Knutti (2015) estimated what fraction of all globally occurring heavy precipitation and hot extremes is attributable to warming, and found that at present day 0.85°C warming above pre-industrial temperatures, 75% of the moderate daily hot extremes over land are attributable to warming. As temperatures continue to increase, and particularly if we overshoot 2°C warming, it is therefore safe to assume hot extremes will rise as well.

Consequences of heatwaves that the IPCC deem likely are:
- Reduced agricultural yields in warmer regions due to heat stress
- Increased danger of wildfires
- Increased water demand and water quality problems
- Increased risk of heat-related mortality
- Reduction in quality of life for people in warm areas without appropriate housing

Heavy precipitation events:
- Increased chance of intense precipitation and flooding due to the greater water-holding capacity of a warmer atmosphere
- Over mid-latitude land masses, extreme precipitation events will very likely be more intense and more frequent in a warmer world
-Likely that precipitation will be concentrated into more intense events, with longer periods of little precipitation in between
- Wet extremes are projected to become more extreme, with mean precipitation expected to increase, and dry extremes are also projected to become more extreme, with mean precipitation projected to decrease

This ultimately leads to a larger disparity between extreme wet and dry areas around the world, which could heavily influence migration. However, many megacities and urban areas are low-lying and therefore vulnerable to coastal flooding due to heavy precipitation events (particularly when coupled with sea level rise).

Overall, increasing global temperatures will likely lead to an increase in the frequency of heavy precipitation events and/or an increase in the proportion of total rainfall from heavy precipitation over many areas, in particular in the high latitudes and tropical regions, and in winter in the northern mid-latitudes.

Consequences of heavy precipitation events that the IPCC deem likely are:
- Damage to crops, soil erosion and waterlogged soils that reduce ability to cultivate land
- Adverse effects on the quality of surface and groundwater, potential contamination
- Increased risk of death, injury, water-borne diseases
- Disruption of settlements, commerce and transport, damage to infrastructure due to flooding

Drought:
- Increased risk of drought globally due to changes in atmospheric circulation, with an increase in the areas affected by drought
- Increased risk of more intense, more frequent and longer-lasting droughts
- Likely lead to food insecurity, water shortages, malnutrition and other socio-economic problems

Warming World: Impacts By Degrees, which is based off the National Research Council report Climate Stabilization Targets: Emissions, Concentrations, and Impacts Over Decades to Millennia (2011), argues that an increase in global temperatures will lead to higher evaporation rates, which can further exacerbate droughts.

The Committee on Climate Change also argue that under a 2°C scenario, an estimated 1.5 billion people each year will live in areas without enough usable water. This of course it not only due to droughts, but also changes in precipitation patterns. However, increasing water stress is a very likely potential outcome of more droughts.

Consequences of droughts that the IPCC deem likely are:
- Land degradation, lower yields, crop failures
- Increased livestock deaths
- Increased risk of wildfires
- More widespread water stress
- Increased risk of food and water shortages, malnutrition, incidence of food and water-borne diseases
- Water shortages for settlements, industry, agriculture, potential for migration
- Reduced hydropower potential

Storms:
- Tropical cyclone activity is likely to be more intense
- Potential for a decrease in the number of tropical cyclones
- Likely poleward shift of storm tracks in both hemispheres
- Likely increase in heavy rainfall associated with tropical cyclones

There is evidence from modelling studies that future tropical cyclones could become more severe, with greater wind speeds and more intense precipitation. Elsner et al. (2008) found that Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been associated to an increase in ocean temperatures over the Atlantic Ocean and elsewhere. Warming global temperatures are likely to result in more intense storms as warm sea temperatures have more energy to convert to tropical cyclone wind. Knutson et al. (2010) suggest that globally averaged intensity of tropical cyclones will increase by 2-11% by 2100, along with a projected decrease in the frequency of tropical cyclones by 6-34%. Finally, Warming World: Impacts By Degrees, claim that hurricane intensity will increase by 1-4% per 1°C of warming and that hurricane destructive power (cube of the wind speed) will increase by 3-12% per 1°C of warming. They also suggest that hurricane frequency decreases by 0-1% per 1°C of warming.

However, these studies and many other models indicate high levels of uncertainty. Some argue that this trend of more intense storms could simply be due to the increase in reporting of tropical cyclones in the past 50 years. In addition, cyclones are difficult to predict due to dependence of cyclone genesis and other phenomena that affect it, such as the El Niño Southern Oscillation (ENSO).

Consequences of storms that the IPCC deem likely are:
- Damage to crops, trees, coral reefs
- Disrupted water supply, potential for contamination
- Increased risk of death, injury, food and water-borne diseases
- Disruption of settlements, loss of property, potential for migration

There are still many uncertainties about the role of increasing global mean temperature in the incidence of extreme weather events. There are also many natural phenomena that can affect extreme weather, such as the El Niño Southern Oscillation, so it can be difficult to ascertain what the potential changes are a result of 2°C warming could be. Finally, natural phenomena can be affected by climate change (and vice versa), such as Cai et al. (2014) suggesting that there is likely to be an increase in the frequency of El Niño events due to "greenhouse warming".

Apologies that this post was not as brief as I had hoped but I'll be back with some quick looks at other impacts of warming past 2°C!

Impacts of Sea Level Rise

I have realised that my post on dangerous sea level rise, which discusses the extent to which sea level could rise under different warming scenarios, does not address the impacts (apart from some pretty scary pictures of submerged cities) it could have on the habitability of Earth (which is, after all, the whole point of my blog). So here's a quick post to fill in that gap.

Cartoon pointing out the lack of plan to mitigate against rising sea levels

A quick Google will tell you that people are seriously concerned of the disappearance of low-lying islands due to sea level rise. A Tech Insider article, has a handy list of 11 islands that are threatened by climate change. The article uses the IPCC's estimate of an increase of 8 to 16 inches (0.2-0.4m) above 1990 levels by 2090, as well as The National Academy of Sciences predictions of sea level increase by 16 inches to 56 inches (0.4-1.4m) by 2100, depending how the Earth responds to changing climate. This list really gives a face to the populations threatened by sea level rise, such as the local population of 325,000 people of the Maldives, which is on average only 1.3m above sea level.

But it's not just the media that are concerned with vulnerable islands. Church et al. (2006) studied historic and projected sea level for tropical Pacific and Indian Ocean islands such as Tuvalu and the Maldives. They estimate that relative sea level rise at Funafuti, Tuvalu is 2 ± 1 mm per year, during 1950 to 2001, with analysis showing that the rate of sea level rise will continue to increase in the future.

Apart from sinking low-lying islands, sea level rise also impacts the contents of the oceans too. With more, and warmer, water in the ocean, ocean pH is predicted to decrease (acidify). The IPCC summarise it as follows:

"The increase in acidity will be higher in areas where eutrophication or coastal upwellings are an issue. It will have negative impacts for many calcifying organisms (high confidence). Warming and acidification will lead to coral bleaching, mortality, and decreased constructional ability (high confidence), making coral reefs the most vulnerable marine ecosystem with little scope for adaptation. Temperate seagrass and kelp ecosystems will decline with the increased frequency of heat waves and sea temperature extremes as well as through the impact of invasive subtropical species (high confidence)."

Coral reefs are indicated to be the most vulnerable marine ecosystem in the face of climate change. Hughes et al. (2003) suggest that projected increases in carbon dioxide and temperature over the next 50 years exceed the conditions under which coral reefs have flourished over the past half-million years. This implies that 2°C of warming would result in the destruction of many coral reefs. Hoegh-Guldberg et al. (2007) also agree with this prediction, using the projections that atmospheric carbon dioxide concentration will exceed 500 parts per million and global temperatures to rise by more than 2°C by 2050 to 2100. These values "significantly exceed" those of at least the past 420,000 years, during which they claim the most extant marine organisms evolved. They predict carbonate reef structures will fail to be maintained under these conditions, and reefs will lose major coral communities.

This is important is coral reefs play an integral part in marine biodiversity, fisheries, tourism, coastline protection, and many other aspects of the ocean and for people on land. Coral reefs provide habitats for 25% of all marine life, so to lose a significant amount of coral communities would likely lead to a loss of equivalent marine life too.

I hope this quick summary of impacts of sea level rise on islands and coral reefs gives a better idea as to why 2°C of warming could render many populations (of people and other organisms) without a home.

We have a Climate Deal!

I know I only posted a few days ago but I wanted to write a quick blog post because I'm super stoked we have a Climate Deal from COP21!!!

I promise I'll be brief but here's the key sentence:

"Holding the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change."

We have a commitment to 2°C! This was both surprising and excellent to hear and I'm glad this is all in writing with the Paris Agreement. On top of this, there was also a commitment to reviews every 5 years, USD $100 billion a year to help poor countries with climate change mitigation, development of carbon markets, forests conservation and support for renewable energy.

However, there still remains to be a lot of work to be done. It's all well and good to say we'd like to keep warming to under 1.5°C, which was the product of some developing countries (such as island states like the Marshall Islands), who also happened to be the most vulnerable due to being low-lying, but how feasible is this?

Well many scientific reports and opinion pieces that have been published today remain positive about this given there are many possibilities. First, we would have to make emission cuts and fast if we want to never go above 1.5°C; but people remain optimistic that this can be a possibility. Particularly as the 1.5°C threshold is included in the agreement, many scientists and interested parties believe this shows the drive to reach this highly ambitious target and the recognition that the difference between a 1.5°C and a 2°C world is substantial. Secondly, and most supported by scientists, we could overshoot 1.5°C and then return to below it, by having negative emissions (due to carbon capture and storage), before 2100. Finally, there are still many uncertainties with predictions of climate under different warming scenarios, plus the uncertainties of how we'll reach that specific warming, which all contribute to the possibility of staying within 1.5°C of warming.

The last thing I want to leave with you is the simple idea that these temperature thresholds (whether it's 1.5°C, 2°C, 4°C or anything else), represent a probability. I really like this idea because scientists have really simplified such a complex response and system down to probabilities of certain consequences. Essentially, the higher the temperature threshold we cross, the higher probability we have of encountering certain detrimental consequences like dangerous sea level rise. And that's all this Climate Deal is about: trying to reduce the probability of dangerous consequences. I hope we continue to move forward from the Paris Agreement with the same amount of optimism, ambition and motivation to succeed.

And with that, I'll leave you with this cartoon that made me laugh:

2 Degrees and Dangerous Sea Level Rise

So while negotiations continue to crack on in Paris for the climate deal (that may never happen but my fingers are crossed!), it's time to go back to my investigation into the potential deadly effects of changes to the carbon cycle leading to 2°C of warming!

Today I'm focusing on all things related to the sea and how 2°C of warming can render parts of Earth uninhabitable. There is obviously A LOT of different studies and things I could talk about so this is just a handful I've found particularly interesting.

There's been some really cool visualisations of sea level rise from 2 degrees of warming recently that I think have made huge leaps in making such a scientific and at times difficult to engage with topic accessible to the public.

Mashable, a popular digital media blog, shared a series of photographs that simulate what 8 locations in the US would like if sea level continues rising (by 5, 12 and 25 feet). Below is one example, using the incredibly iconic view of the Statue of Liberty.

The photoshopped scenes were created when Nickolay Lamm saw an article in the New York Times, that depicted sea level rise on maps of different areas in the US. Again, this article helps people understand the local effects of sea level rise, and the descriptions point to specific areas people would actually care about. For example, for New York City, the description reads "Large portions of all five boroughs are gone, including much of Manhattan below 34th Street". This is why I strongly believe this kind of scientific communication is vital for getting public and political support on climate change mitigation.

Another great sign is that this communication isn't slowing down. Climate Central, albeit more scientific than Mashable or national newspapers, is a real-life example of scientific communication geared towards the general public. (See their article for a drag comparison of 2°C and 4°C warming on sea level in major cities around the world, also created by Nickolay Lamm) I particularly love their use of Google Earth to create fly-over videos of sea level rise in many coastal cities around the world. As I grew up in Hong Kong, definitely a coastal city at major risk of high sea level rise, I found it really scary to see buildings I know become inaccessible due to water under 4°C and 2°C scenarios. I think it conveyed a sense of urgency and disaster that perhaps numbers and model predictions just don't quite do.

So how convincing are the arguments that 2°C will result in these sea level rises that are enough to seriously damage coastal cities?

There's been studies on future sea level (rise or even fall) for many years now but I'd like to just talk about a few recent ones as they use new technology (such as laser altimetry) and build upon historic studies.

The main focus of sea level studies is on ice sheets and the temperatures required to cause dangerous melting of ice sheets (such as the Antarctic or Greenland ice sheets). First, this very new study from Golledge et al. (2015) focuses on the Antarctic ice sheet and uses an ice sheet model to estimate sea level rise under 1.5 to 2°C warming. The study (like many others) uses the IPCC's representative concentration pathways (RCPs) as the input variable for greenhouse gas concentration trajectories. Across all 4 RCPs, global mean sea level is projected to rise by 0.26 to 0.82 m by the late-21st century. However, Golledge et al. argue that this underestimates sea level rise in the long term and doesn't take into account polar amplification, which can "can lead to surface air temperatures, and ocean temperatures, that may be as much as double the magnitude of the global mean perturbation". 

This study argues that 3 out of the 4 RCPs (excluding the lowest warming projection RCP2.6), "the future commitment to a rise in sea level from Antarctica is substantial", and loss of major ice shelves within 100-300 years. Sea level rises are predicted to be substantial, such as 0.1–0.39 m by 2100 under RCP8.5 (mean warming of 2°C by 2065). Scarily, they predict that rates of sea level rise are 5.5-15 mm per year by 2300 under RCP8.5, but even under the lesser RCP4.5 and RCP6.0, reach 3-5 mm per year by 2300. Golledge argues that there is a "commitment" to sea level rise due to "the collapse of buttressing ice shelves" that creates an ice-sheet response that greatly increases grounded ice discharge for centennial or millennial timescales, even if greenhouse gas emissions are reduced and temperatures stabilise. These findings, although based on computer models, which are bound to have any number of uncertainties, really hit home the phrase that has been thrown around a lot around COP21 this past week: "We are the first generation to feel the impact of climate change, and the last generation that can do something about it".

Secondly, I'd like to share a study I read about Greenland ice sheet and sea level rise. Now the Greenland ice sheet, much like the Antarctic ice sheet, still has a lot of uncertainty attached to how it will react to temperature but has the potential to cause huge fluxes in sea level. NASA claims it contains 8% of all freshwater on Earth, and if it melted in its entirety, would single-handedly cause a sea level rise of 23 feet (7 m). So a slightly important geographical feature.... 

A study by Csatho et al. (2014) published just over a year ago, using the new technology of laser altimetry, focuses on measuring ice thickness to understand the complex dynamics of the Greenland ice sheet. The study period was from 1993-2012 and used nearly 100,000 points to determine elevation and changes. The main finding of their study was an estimated mean annual ice sheet mass loss of 243 ± 18 Gt per year, which resulted in 0.68 mm sea level rise per year for 2003–2009. Another, slightly older study by Robinson et al. (2012), estimates that the temperature warming threshold for a "monostable, essentially ice-free state" is 1.6°C, not 3.1°C as previously estimated. They also suggest that for "sufficiently high initial temperature anomalies", losing the entire ice sheet becomes irreversible.

Again, there are huge uncertainties regarding the future of ice sheets and their impact on sea level rise but there is a general consensus that preventing huge loss of ice from both the Antarctic and Greenland ice sheet starting as early as possible is important for combating the threat of dangerous sea level rise.

Most recently, a summary report from Climate Central, suggests that 2°C of warming would "lock-in" 4.7 m of sea level rise by 2100 and therefore submerge land home (in 2010) to 280 million people globally. This translates to 5 out of the 10 megacities with the highest populations being affected (and all in Asia), including my home Hong Kong. This is scary, but hopefully will motivate Asian nations (particularly China, who is the biggest emitter of greenhouse gases in the world and in which 2 of the 5 vulnerable cities reside) to stay within 2 degrees and reduce damages as much as possible.

Finally, I wanted to include this counter-argument that came around a few months ago from NASA, that the Antarctic ice sheet has overall seen a gain rather than a loss. The results claim that Antarctica is not currently contributing to sea level rise, but is taking 0.23 mm per year away, which means the IPCC's estimate of 0.27 mm per year of sea level rise attributed to Antarctica is being removed elsewhere.While it is horrifying that people use this one study as an argument that climate change is a hoax, it presents some interesting challenges in accurately measuring and modelling changes to complex climatic features such as ice sheets.

Thanks for reading and next time I'll be looking at some other effects of emission levels high enough to create 2°C of warming!

COP21 - Is there any hope?

Having just had a super interesting workshop on COP21 to understand the complexity of the negotiations on an agreement to limit global warming to 2°C, I'd like to go a little off path and spend this blog post exploring the whether there is any hope of limiting warming to 2°C.

Firstly, before COP21 even began, many nations submitted Intended Nationally Determined Contributions (INDCs) that detailed out, in varying degrees of specificity, their plans for 2050 to tackle climate change and ensure global warming limited to 2°C. 158 INDCs were submitted and included time frames and/or periods for implementation, scope and coverage, planning processes etc. Climate Action Tracker analysed 19 of these documents, covering about 71% of global emissions, to come up with an estimated global warming of 2.7°C, which means a failure to keep to the internationally agreed 2°C target. They also rated the INDCs as either inadequate, medium or adequate, with only 2 of 19 INDCs rated as adequate: Ethiopia and Morocco, covering 0.7% of global emissions. Dishearteningly, the 8 INDCs rated as inadequate are all "developed nations", including Australia, Japan, Canada and Singapore. This means their plans are "not considered to be a fair contribution to limiting warming to 2°C from almost any perspective. Alternatively, the rating of medium means plans (including USA, the EU and China) are "consistent with 2°C, according to some perspectives on their fair-share contribution, but they still rely on others to have more ambitious
targets in order for the world to hold warming to below 2˚C".

Country ratings and share of emissions from Climate Action Tracker analysis of 19 submitted INDCs

These results were very discouraging to me, particularly as the most powerful nations (who are also the biggest emitters) are relying on other nations leading the way in ambitions for limiting warming to 2°C. Surely this needs to be reversed if we are to actually make our targets and enforce these plans?

One interesting idea that I've encountered in reading up about COP21 is the "ratchet mechanism". Carbon Brief wrote a great introductory article about it. Essentially, the ratchet mechanism entails new plans and targets being created every 5 years, with increasing ambition and increasing actions. In this way, even though the current plans do not lead to 2°C, hopefully after a few reiterations of INDCs, plans will be made to keep to 2°C before it actually happens. This is an idea many are clinging onto as it means the proposed plans of the INDCs can be used and we can still keep to 2°C by 2100 if the ratchet mechanism is used. In many ways, the ratchet mechanism is good in that it will encourage strong, legally binding review processes, as they will be required in order to keep 2°C as the long term target.

Nevertheless, I'm unconvinced. If we can't come up with a long term plan to keep to 2°C now, at Paris, where the world has come together, there's no concrete way to know we will ever make the plans to ensure 2°C. Additionally, these plans, however ambitious, are still plans. How realistic they are and how feasible, remains to be seen. Although there has been promising progress, and nations such as the EU are on course for their climate targets, more needs to be done. With more ambitious changes and overhauls of processes that are well-established, such as using coal, I'm unsure how well nations will be able to stick to their targets, and this needs to be accounted for. I'd prefer if nations aim high now and then adjust realistically as they encounter changes, than to never aim that high and never reach any semblance of preventing the consequences of 2+°C.

One of the arguments against very ambitious targets is the technicalities required. For example, our simulation workshop stipulates that an emission decline rate of 3.5% is the upper limit, as anything higher than that could potentially lead to economic instability, amongst other dangers. This argument is probably the most persuasive for me, but that doesn't address the fact that this limit will likely remain in the future, thereby restricting targets both now and in the future.

Sir Brian Hoskins, a climatologist from Imperial College London, explained that hitting peak emissions early is important, as it means there is a lower cumulative volume of CO2 in the atmosphere which will make it easier to remain below 2°C warming. If a climate agreement isn't ambitious enough in its peak emissions date, there is more accumulated CO2 to deal with, meaning there may be the need for carbon capture and storage technologies or other removal techniques. This sounds promising but in reality, the technology does not exist yet, and who knows when it will be available and viable? However, the International Business Times article from which Brian Hoskins is mentioned, reveals that there may be some hope. The article states that there is a chance that greenhouse gas emissions have fallen for 2015, marking the first time there is a drop in emissions in the "modern era" (presumably post-industrial). This revelation, in conjunction with the knowledge of economic growth for 2015, is a cause for optimism, as it indicates that cutting emissions and economic growth are not mutually exclusive.

Hopefully the representatives of the many nations at COP21 will take these pieces of news into account when creating a climate change agreement, and build upon the progress from COP21 when returning to their homes.

If it seems I am pessimistic about a clear outcome of COP21 that will successfully keep us below 2°C of warming, it is because I have yet to see explicit evidence that this can and will happen. Even in our COP21 simulation workshop, with our individual geographer biases, we failed to reach a negotiation that enabled a 2°C rise only (we got to 2.7°C). Just today, the BBC is reporting criticism for the UK as they are looking like they will fail to follow through on the big talk of David Cameron at COP21. According to them, the UK's climate policies have changed in recent months by George Osborne, for the worse, not the better. For example, £1 billion for a CO2 capture demonstration plant was recently cut; along with cutting many subsidies for renewable energy.

With the majority of the general public agreeing that climate change is now a real threat, I think it's time for leaders to step it up with their plans for climate change; and to make these plans legally binding in order to ensure all this work isn't all talk. We'll see how things turn out.

Does 2°C make Earth uninhabitable?

In the spirit of making my blog name somewhat relevant to this module and the theme my blog is following at the moment, today I'm looking at arguments that a mere 2°C increase in temperature will render Earth uninhabitable for humans (and perhaps for other species).

There are many aspects of an environment that make it an appropriate habitat for a species. So I'm only going to look at a few different factors that I think are important for life to exist on Earth. For this blog post, I'll be looking at temperature as the basic limiting factor for habitability of regions for humans and other animals.

Below is a diagram demonstrating the range of temperatures and relative humidity that are comfortable for humans. The temperature range is from around 20°C to 30°C, and is an indication of indoor air temperature, but depends on relative humidity as well. This makes sense, as 30°C with relative humidity of 60% would be highly uncomfortable, but 30°C with humidity of 30% would be more comfortable. Humans maintain a core body temperature of around 37°C, even within highly variable climates; and human skin is strongly regulated at 35 °C or below, because the skin must be cooler than body core in order for metabolic heat to be conducted to the skin. Sustained skin temperatures higher than 35°C imply hyperthermia, which can be dangerous for health.




Outdoor air temperatures endured by humans around the world today are obviously a much larger range than the graph above. However, these temperatures are neither sustained naturally nor are humans exposed to these temperatures for extended periods of time. Humans have also found adaptations for living in extreme temperatures, such as air conditioning and central heating. Even with these adaptations, mounting evidence indicates that temperatures will only get higher, and the Met Office even claims that 2015 is likely to be the hottest year on record, and on average 1°C than pre-industrial levels.

So how much is rising temperature a threat to human survival? An article in CNN recently ran this sensationalist headline: "Persian Gulf heat: It may become too hot for humans to survive, study warns", and the study cited, focuses on southwest Asia, a region already experiencing extreme temperatures. The study claims that many cities need to support global mitigation strategies to enable the IPCC climate change projection pathway of RCP4.5, rather than RCP8.5 which is the business as usual approach. If this happens, under simulations, the maximum temperature threshold is never reached, and although temperature will be higher, these regions would not be uninhabitable. However, they claim that near the cities of Jeddah and Mecca, important religious grounds, are a mere 2°C away from reaching the temperature threshold, and therefore there are certainly vulnerable areas that require immediate action to prevent the warming that would otherwise occur.

The authors of the study, Jeremy Pal and Elfatih Eltahir, base a lot of their assumptions about the temperature threshold on another study, by Steven Sherwood and Matthew Huber. This study looks at the limit of adaptability to climate change due to heat stress, as measured by wet-bulb temperature, which is a measure of both temperature and humidity. Their study uses six-hourly 2-metre temperature, humidity and pressure data from the ERA-Interim dataset to determine wet-bulb temperature, which so far never exceeds 31°C. Based on the assumption that human skin temperature of 35°C for a sustained period of time would cause hyperthermia, they suggest that a wet-bulb temperature of 35°C is the upper limit for adaptation to climate change, as humans and other mammals would not be able to dissipate metabolic heat. Therefore, if a region had a temperature of 35°C for an extended period of time, it would be "unlivable". Sherwood and Huber also stress that adaptations such as air conditioning would not be "satisfying, affordable, and effective for most of humanity" as power shortages would be life threatening, and humans would be limited to staying in the safety of air conditioned areas.

While I find Sherwood and Huber's study elegant, it concludes that an average global warming of 7°C would be needed in order for there to be areas with 35°C wet-bulb temperatures for an extended period of time. A warming of 11-12°C would encompass most of the areas humans live in now. Therefore this average warming needs to be much higher than 2°C in order to have dire effects. But this study shows how temperature in isolation can be a threat and that this potential result of climate change deserves some attention on its own. They emphasise this with the statement: "If warmings of 10 °C were really to occur in next three centuries, the area of land likely rendered uninhabitable by heat stress would dwarf that affected by rising sea level".

These two studies on temperature as a limiting factor for the habitability of areas on Earth serve to stress the importance and urgency of finding a solution to limit mean warming to as low as we possibly can, and of implementing mitigation measures as soon as possible. This is all too relevant in the lead up to COP21 in a mere 4 days and I'm sure the world will be waiting with bated breath for the results.

Next week I look forward to exploring other impacts of a 2°C rise in temperatures and whether they might render Earth uninhabitable!

P.S. Another interesting idea is that climate change can make Earth uninhabitable because it can be a cause of conflict. Earlier this week, Sky News released a video interview with Prince Charles, where he mentioned the 2 degrees threshold, and how the drought in Syria is partly to blame for the conflicts there. I won't be exploring this further as I don't believe it's possible to quantify the impact of climate change or warming on conflict, but it's interesting to consider that climate change can affect complex human interactions.

Using energy to limit 2 degrees

In my last post, I spoke about the 2°C rise limit that is more or less agreed will limit "dangerous" consequences of climate change. In reality there is no hard limit but nonetheless it's an important figure for political, social and scientific reasons. The more difficult part to quantify is the question of how we will endeavour to prevent 2°C rise. There are many areas that could fall into the answer to this but this blog post will focus on energy, and therefore fossil fuels.

Since I've mentioned the IPCC Fifth Assessment Report in almost every other blog post, let's begin by looking at their chapter on Energy Systems in the report on Mitigation of Climate Change. The reason energy is included under mitigation of climate change is split into 5 sections: Fossil fuel extraction, conversion, and fuel switching; Energy efficiency in transmission and distribution; Renewable energy technologies; Nuclear energy; and Carbon dioxide capture and storage (CCS). They state that "climate change can only be mitigated and global temperature be stabilized when the total amount of CO2 emitted is limited and emissions eventually approach zero", and that the energy supply sector is the largest contributor to global greenhouse gas emissions, hence energy places a large role in preventing the 2 degrees scenario from being reached.

The ways energy can aid the prevention of the 2 degrees scenario include decarbonisation, increasing energy efficiency and geoengineering. The Carbon Brief's article is an excellent summary and brief introduction to these ideas.

1) Decarbonisation of energy

This method means moving towards a system that uses energy that does not emit any carbon dioxide to the atmosphere and therefore will significantly reduce the human impact on climate. General discussion of energy in the context of climate change focuses on this method, and particularly on transitioning from a fossil fuel dependent world to a fossil fuel independent world through the use of renewable energy. Although this seems straightforward enough, the presence of fossil fuels still remains massive on a global scale, and many economies and societies have not ventured into decarbonisation just yet. There is definitely hope though, as fossil fuels and renewable energy are currently hot topics, and with COP21 on the horizon,steps have (hopefully) been taken to include decarbonisation on the agenda for many countries and their policies.

The role of National Geographic and many other climate focused organisations and websites such as the Carbon Brief help to put a spotlight on the developments in decarbonisation of energy and wider climate issues. For example a recent article from National Geographic examines the cities closest to running entirely on renewable energy sources. It's an important reminder that, amidst the widely broadcast country level energy and policy discussions, change can and is already happening at the city level and at even smaller scales.

The Carbon Brief is a great source of information on studies and other scientific discoveries that are accessible to the general public and the focus on the role of carbon in global climate change, much like this blog! In an article, they synthesise the study of Christophe McGlade & Paul Ekins on the role of coal in the energy industry for the future. McGlade and Ekins suggest that, in order to stick to under 1100 gigatonnes of carbon dioxide emitted between 2011 and 2050 (I discussed this idea of a carbon budget in the last blog post) and thus within 50% chance of staying under 2°C rise, 1/3 of oil reserves, 1/2 of gas reserves and over 80% of current coal reserves should remain unused. If we ignore this and use all of the world's known oil, gas and coal reserves, the carbon budget would be three times the recommended amount. The graphic below shows a breakdown by 10 specific regions.

Interestingly, the paper discusses the use of gas as a way of transitioning to a carbon-free world, as approximately 94% of Europe's gas reserves are "burnable" under a 2 degree scenario. However on a global scale, meeting the 2 degree commitment in a cost-effective way means leaving 100% of unconventional oil and 82% of unconventional gas resources unburned, according to the model. These numbers emphasise the need for a global commitment to transition to low or zero carbon energy, and quickly.

The good news is, this is the expected future. The International Energy Agency published their medium-term report in October 2015 that forecasts that 26% of the world's energy supply will come from renewable energy sources by 2020 (a mere 5 years away!). Sweden leads the way towards becoming the world's first fossil-free nation, through increasing the budget for renewable energy. China, though currently the world's biggest producer of carbon emissions, is responsible for 40% of global renewable capacity growth, and with the help of global commitments, the desire to have energy security, as well as economic incentives, many of the world's worst carbon emitters could be turning things around.

2) Increasing energy efficiency

Along with decarbonisation, another method that could help mitigate climate change of 2°C is increasing energy efficiency. With growing technology, this may seem straightforward; however the global population and therefore demand for energy is still increasingly rapidly. By 2040, the World Energy Outlook estimates that total population will hit 9 billion, and global wealth is expected to double. Without any policies, this growth would lead to a 50% increase in energy usage, but if we are to keep to the 2 degree scenario, energy demand can only increase by 17%. In order to limit energy use, the world would need to become twice as productive. Regulations play an important role here, with policies needed to drive energy efficiency, such as ending fossil fuel consumption subsidies and consumer product efficiency standards to be enforced.

A good example of this is in the recent Volkswagen scandal (although with nitrous oxide not carbon dioxide). Had Volkswagen adhered to the Environmental Protection Agency's standards for carbon emissions from their cars, a potential 237,161 and 948,691 tonnes of NOx emissions could have been avoided, according to The Guardian.

Diana Ürge-Vorsatz & Bert Metz summarise the role of energy efficiency in a paper in the aptly named journal Energy Efficiency. They state that energy efficiency has played a key role in reducing society's CO2 emissions, particularly in the last decade, and will likely continue for the forthcoming decades. The paper draws on the IPCC's Fourth Assessment Report and stipulates that improved efficiency is likely to be a key focus in the short term, before shifting to low-carbon energy sources as costs for energy improvement grow while decarbonisation costs decrease in the longer term. The sectors with the biggest potential for energy efficient are building, transport and industry.

Therefore because in the planning and preparation for a zero carbon future, steps must be made to transition easily and with as little economical impact as possible, energy efficiency is an important player.

3) Geoengineering

Carbon capture and storage (CCS) is a method of removing carbon emissions before they are released, which could enable negative carbon emissions (released, not necessarily cumulative, it must be noted). This is directly related to energy as it utilises fossil fuel plants and has the greatest potential for use in the energy sector. I intend to explore this topic in more depth in the future but this method of mitigation has the potential to alleviate some of the pressures of rapid decarbonisation that is needed to fit within the 2 degree scenario.

4) Other mitigation solutions

There are potentially a whole multitude of ways to mitigate climate change to stick to 2 degrees that have yet to gain traction or yet to be discovered. A simple one would be to enforce reductions of energy usage, irrespective of the source, which is hopefully on the agenda for COP21, and the many technologies evolving and advancing as we speak (well as I type) can definitely help. One of my many hopes for the future is the transition to a world that only uses electric cars, led by the brilliant Elon Musk and Tesla (have a read of this article, if you have some time to spare).

I hope this gave some insight into how energy plays such a key role in our journey to keep temperatures below the all-important 2°C. There is still a lot to be done before we can wipe our brows and breathe a sigh of relief that we are no longer on the path to an uninhabitable planet, but if changes are put into motion soon (like COP21 soon), there is undeniably some hope for humanity.

2 Degrees Too Far?

As I sat thinking of what I could delve into in the huge area that is the carbon cycle, I was reminded by countless news articles of the importance of one figure: 2°C of warming. This figure relates to an average rise in global temperature due to increased greenhouse gas emissions (with a lot of emphasis on carbon dioxide) and I think it could be an interesting avenue to explore with regards to climate change due to the carbon cycle. So the evolution of this blog is likely going to focus on research around 2°C and this post is an explanation of where the figure of 2°C came from (why not 1°C? 3°C? 2.367°C?), how it became the household phrase people use as a measurement of climate change, and whether it is the hard-line threshold for not venturing in uninhabitable territory.

The figure of 2°C temperature rise has been thrown around in talks of climate change almost as much as phrases like "global warming" and "carbon credits". This figure is so prolific that it's difficult to pin down the exact source of 2°C as the limit of global temperature rise, relative to the pre-industrial average, that avoids "dangerous climate change". Below is a nice selection of historical references to 2 degrees.

There was a distinct boom in discussion of climate change, or "global warming" back then, in the late 90s/early 2000s, and 2 degrees featured heavily. Many stakeholders, from scientists to politicians, were talking about climate change impacts under 2°C rise, and what we might do to avoid 2 degrees. Notably, countries were coming together to talk about the environment, with agreements like the Kyoto Protocol and the UNFCCC (United Nations Framework Convention on Climate Change).

Even within this month, in 2015, 2 degrees continues to dominate discussions of climate change and impacts. Mentions in current news stories include coral reefs, Antarctic ice shelves, the ocean food chain, wildlife, deserts, weather-related disasters, and most disturbingly, loss of habitability for humans. I also watched this Ted talk recently by climate change and energy researcher, Alice Bows-Larkin. In it, she mentions 2 degrees, and how this commonly discussed limit has left scientists divided into two groups; those who believe we have no chance of surpassing 2 degrees, and those who cling on to the small chance that we can avoid 2 degrees.

As part of this discussion, climate projections and models have looked at how different CO2 levels might affect temperature, and how that could impact multiple areas in the environment and for humans. Just like the 2°C threshold for temperature, some scientists suggest a threshold for CO2 concentrations of 500ppm, and various metres of sea level rise.

So the question remains, can Earth avoid the 2°C change that might render large parts uninhabitable?

According to the IPCC's Fifth Assessment Report in 2013, the globally averaged land and ocean surface temperature between 1880 and 2012 shows a warming of 0.85°C. They state that it is "virtually certain" that globally the troposphere has warmed since the mid-20th century. Alarmingly, they also state that it is "extremely likely" that that more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and other anthropogenic changes.They use different scenarios to model changes, and under all but one, global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850 to 1900. This does not paint a particularly optimistic picture for avoiding 2 degrees, and they suggest that limiting these changes will require "substantial and sustained" reductions in greenhouse gas emissions.

Interestingly, they also point out that while increasing CO2 will create changes in climate, climate change will in turn affect the carbon cycle, to further exacerbate the increase of CO2 in the atmosphere. In my last post I mentioned balance in the carbon pools, and it is likely that climate change will cause increases in uptake in some pools (ocean) and potential decrease in others (land uptake, although there is a great deal of uncertainty). Carbon, and in particular CO2, therefore plays a hugely important role in whether or not we will be able to avoid 2 degrees.

Since CO2 is cumulative, global emissions of CO2 over time need to be known to understand the effects. The term carbon budget was coined as a way to predict the amount of CO2 emissions we can emit while still having a likely chance of limiting temperature rise by 2°C. A report in 2013 by Carbon Tracker suggests that a carbon budget of 900 gigatonnes of CO2 gives us an 80% probability of avoiding 2 degrees. This means that a large amount of fossil fuels are "unburnable", and the carbon budget is particularly constrained after 2050, where, unless we can create negative emissions, only 75 gigatonnes of CO2 can be emitted to give us an 80% probability of avoiding 2 degrees. This is equivalent to 2 years of emissions at current (2013) levels. The IPCC proposed a carbon budget of 1000 gigatonnes of CO2 starting from 2011, that would give us a 66% probability of avoiding 2 degrees. I'll admit when researching these numbers, I slowly felt my optimism dropping. With current estimates and use of about 35 gigatonnes of CO2 a year, we'll likely use up our carbon budget by 2034, thus leading to those 2°C we've been so intent on avoiding. By 2100, we would've reached 4°C warming, which has even more dire impacts. So right now, the outlook for avoiding 2 degrees doesn't look so good.

The one thing that could avert all this is something radical. A study by Peters et al. (2013) claim that "immediate significant and sustained global mitigation" is needed to avoid 2 degrees, with a probable reliance on net negative emissions for the longer term. They found that some countries have reduced CO2 emissions over 10-year periods, through a combination of (non-climate) policy intervention and economic adjustments to changing resource availability. In the UK, shifts to natural gas, therefore substituting oil and coal, have led to sustained mitigation rates in the 1970s and 2000s. Mitigation strategies focus on fuel substitution, efficiency improvements, and look towards the growing technology in negative emissions. Finally, they emphasise that this is a current and pressing issue, as global mitigation efforts need to be put in place as soon as possible, or soon, our efforts will be futile in avoiding 2 degrees.

There's no way we can know for sure that we'll be able to avoid 2°C, but we haven't given up. Just a few days ago, the executive secretary for the UNFCCC, Christiana Figueres stated that "we are not giving up on a 2 degree world", believing that we can develop processes to ensure this. With COP21 on the horizon, there definitely remains some scope for optimism, and Figueres believes the changing energy industry will play a major role. Kevin Anderson of the Tyndall Centre for Climate Change Research echos this sentiment, although he suggests that the IPCC claims that global economic will be unaffected are unrealistic. He suggests that if we are to meet our 2 degrees target, high emitting (and wealthy) countries will need to drastically cut their energy use and overall consumption. Next week I'll be exploring how energy could help us avoid the 2 degrees crisis.

The Carbon Cycle

Hello!

Apologies for not posting earlier; I was trying to focus my blog down into an area of interest in terms of global environmental change and what could make a planet uninhabitable.

I've decided to focus on one particular area of the environment: the carbon cycle. I aim to explore the question: how are humans impacting the carbon cycle to affect the habitability of Earth? Astrophysicists Henning and Salama (1998) state the importance of carbon, particularly for evolution as it is the fourth's most abundant element in the universe and has the ability to form complex species. As such, carbon is a key element on Earth and can influence many different areas. I'll be exploring changes in the carbon cycle and the effects on both the environment and on humans.

This post is to give a brief introduction to the carbon cycle and its role as a major part of Earth's environment.

What is the carbon cycle?
Have a quick look at this Crash Course video that nicely introduces the carbon cycle (start at 1:02).

As Hank Green so eloquently put it, carbon is "the stuff of life, so the carbon cycle is a whole bunch of things living and dying, and in the process, swapping carbon". Below is a nice and simple graphic that displays the different carbon stores on Earth and the processes that lead to carbon being swapped between stores.

Some of the ones of particular note are carbon in vegetation, which humans are altering rapidly; as well as coal, oil and gas or carbon extracted and used as fossil fuels to emit carbon back into the atmosphere. This is heavily influenced by human activity, which leads me nicely on to my next question:

Why do changes in the carbon cycle matter?
I've briefly outlined what the carbon cycle is, but why does it really matter if it changes? Well, I personally see it as a matter of balance. As the diagram shows, carbon is stored and moves around in many areas, but if one store grows much larger relative to other stores, this throws the balance of carbon completely off and can have huge consequences. NASA's Earth Observatory website states that the balance of the carbon cycle acts "like a thermostat", helping keep Earth's temperature relatively stable.

In the history of Earth, variations in the carbon cycle have been a result of Earth's orbit, which changes the amount of energy Earth receives from the sun, and therefore the climate of the Earth. Glacial periods have slowed the carbon cycle and interglacial periods speed up the carbon cycle. However, in recent years (exact time debatable), humans have had a significant impact on the carbon cycle. Many scientists debate this new and unnatural epoch, named the Anthropocene, as the time period with which humans have wrenched Earth out of its natural cycles of warm and cold, and carbon is in the centre of this change. As humans change the carbon cycle, this has a ripple effect across the environment.

Hence, changes in the carbon cycle have widespread effects on different areas in the environment. For example, Schlesinger et al. (2000) have studied soil as a pool (or store/reservoir) of carbon and concluded that human activities, particularly cultivation, have reduced the pool of carbon in soils and transferred it to the atmosphere. This is likely to further exacerbate the greenhouse warming effect of carbon in the form of carbon dioxide in the atmosphere, with further consequences related to the rising temperature of the Earth.

While many changes in the environment could make Earth uninhabitable for humans and many species, I sincerely hope humans aren't changing the carbon cycle to this detrimental consequence and only time will tell if we are beyond the point of no return. I hope this brief introduction to the carbon cycle sets the context for its importance in the changing global environment and I'll be looking to explore further within specific aspects of the carbon cycle with how they are changing and what effects this might have.

Thanks for reading!

Welcome to my blog!

Hello!

My name is Kaitlin and this is my blog. I suppose this is a test post, as I haven't prepared any amazing insights into environmental change or anything like that. Instead, I'm looking to introduce this project and set the scene for what I aim to explore. 

As my blog name suggests, I'm interested in the idea of environmental change rendering Earth as uninhabitable, for humans and perhaps for other species. (Side note: why do 'inhabitable' and 'habitable' mean the same thing? And why isn't 'unhabitable a word? I genuinely feel I have an unnecessary amount of vowels in my URL because of this.) I recently watched the movie The Martian, and read some fascinating articles on Mars and the concept of colonising it, and gained a new appreciation for our own funny little planet that has just the right environment to sustain a whole plethora of life. I also feel constantly inundated by new information about how Earth is changing and affecting all of us on it. This is therefore a way for me to explore more about this topic and create a voice in the sea of opinions. 

I'm undertaking two modules that require me to blog and The Inhabitable Planet is for my module GEOG3057, Global Environmental Change! I'll be exploring the effects of environmental change on anything that could threaten the sustainability of life on Earth. Perhaps I'll focus on a particular area of interest after doing some research, but for now that's what I'm going with. 

That's about all I've got for the time being. It's a Sunday night so I'm going to test this blog post out and get to work on content! I'll be writing at least once a week so come back next week and see how I've kickstarted this project. 

P.S. This is Mars, a (currently) uninhabitable planet, looking a little scarily like Earth.