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.