2010 Russian Heat Wave

In 2010 large swaths of the earth were hit by extreme weather in the form of heat waves. The effects were particularly strong in Russia, where numerous records for the hottest day across the country were broken (or smashed in some cases). Over 50,000 deaths were reported in Russia (Khandekar et al., 2013), and according to the Guardian, temperatures were around 10C above their seasonal average and there were substantial damages to the wheat harvest, costing the Russian economy $15bn. The cause of the heat wave was a blocking anticyclone over Russia, that was maintained by "anomalous cyclonic conditions over the Mediterranean area" and a similarly anomalously strong monsoon circulation (Trenberth et al., 2012). This blocking high lead to a temperature inversion which trapped exhaust fumes close to the ground, leading to some pretty horrendous conditions in Moscow:

Moscow on the 17th of June and 10th of August

From this it's clear that the human costs of extreme weather can be devastating, even when the extreme weather is not in the form of a one off extreme event such as a hurricane or a flood. The question of attribution of these events is therefore hugely relevant to the debate on climate change, because if it were to be shown that these events were caused by a warming climate, then this would directly link anthropogenic influences to huge economic and human costs.

How can a single event be attributed to a warming climate?

It is notoriously difficult to attribute a single given event to climate change. Indeed, it may well be a futile task, here is part of a paper examining the role climate change had on the 2003 heat wave in Europe (Stott et al, 2005): 

It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate—for example, increasing concentrations of greenhouse gases in the atmosphere—because almost any such weather event might have occurred by chance in an unmodified climate.

The paper goes on to examine the link between increased global temperatures and the risk of a given event happening. That is, assuming that there's no direct connection between the event and global warming, rather there's a possibility of increased statistical likelihood that the event was caused by climate change. They find that this was the case for the 2003 heat wave in Europe, through a method of comparing the temperature in 2003 against a number of simulations using the HadCM3 model for the same area and seeing if the value was outside of statistically significant levels.

Was there a greater risk of the 2010 Russian heat wave because of a changed climate?

In this paper: Was there a basis for anticipating the 2010 Russian heat wave? (Dole et al., 2011), the authors find that "the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability". They use a range of techniques to draw this conclusion, using CMIP3 models and also comparing the heat wave temperatures against historical temperatures for the region. Indeed, this provides the main evidence for their conclusion about the attribution of the event to climate change, making it differ slightly in its methodology to Stott et al. (The model simulations were more involved in trying to hindcast the event than as part of the study of attribution.) This means that their approach for attributing 'blame' is mainly empirical in nature, as opposed to the more model orientated methods used in Stott et al.

Conclusion

It's impossible to say that any one event was 'caused' by climate change. However, it is perfectly reasonable to apportion an amount of blame to climate change, as was done by Stott et al. for the European heat wave. Whereas for the Russian heat wave it is "very unlikely that warming attributable to increasing greenhouse gas concentrations contributed substantially to the magnitude of this heat wave". So is it fair to say that the 2010 heat wave had no link to climate change? On the face of this post's evidence, yes, but things aren't always clear cut in science, and in a future post I'm going to have a look at a paper that finds itself in explicit contradiction to the Dole et al. paper, and see if there's any way of resolving this apparent contradiction.

EDIT:

See this post then for the next in the series, and this post for the final instalment.

Climate Change and the conditions for increased hurricane and typhoon activity

After last week's devastating typhoon, I'm going to have a look at the connection between global warming and increased tropical cyclone activity (both hurricanes in the Atlantic, and typhoons in the Pacific). From a logical standpoint, it makes sense that if there is more energy in the ocean and atmosphere systems in the form of higher temperatures, then the available energy for these super typhoons will be higher. So you would expect that there would be both more frequent and stronger typhoons. Following an article in The Guardian on Typhoon Haiyan and its links to climate change, I'd like to look at some of the evidence for this linkage.

Tropical cyclones and climate change

When looking at tropical cyclones in relation to climate change, it is normal to look at both their intensity and their frequency. This IPCC SREX summary report states that there is low confidence in any increases in frequency or intensity of these events:

There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities.

However, in a recent paper: Downscaling CMIP5 climate models shows increased
tropical cyclone activity over the 21st century  (Emanuel, 2013), a case is made that both the intensity and the frequency of tropical cyclones could increase over the next few decades. This paper uses 6 models from the CMIP5 ensemble of General Circulation Models (GCMs), and downscales them (embeds a model of finer resolution into the GCM) so as to be able to better resolve the storms themselves. From the paper:

One distinct advantage of our downscaling technique is that it captures the full spectrum of storm intensity

From this, they conclude that running the model at a higher resolution provides a better estimate for the overall storm intensity. The results that they found, namely that intensity and frequency will increase by 8-80% and 11-41% respectively, are interesting because they are at odds with a similar study carried out on an early generation and current generation models - CMIP3 and CMIP5 - in this paper: Dynamical Downscaling Projections of Twenty-First-Century Atlantic Hurricane Activity: CMIP3 and CMIP5 Model-Based Scenarios (Knutson et al., 2013). In this paper, the CMIP3 models showed that the intensity of storms would increase by 87%, but that the frequency of tropical cyclones would decrease by 27%. The more recent CMIP5 models found similar results: storms would increase by 39-45% and frequency would decrease by 20-23%.

In an earlier review article: tropical cyclones and climate change (Knutson et al, 2010), both current (in 2010) generation models run at normal resolution, and higher resolution models are considered. It finds that high-resolution models project that storms will become stronger by 2-11% by 2100, which is in qualitative agreement with the above papers, but the magnitude of the change is much smaller. It was written before both of the above papers, which could explain the discrepancy. The article goes on to say that for the current generation of models, storm frequency is projected to decrease by 6-34%. Whereas higher resolution models "project substantial increases in the frequency of the most intense cyclones". The article points out that the use of downscaling can have a noticeable effect on the results in terms of frequency of stronger storms:

There is a clear tendency among the models, particularly at higher resolution (60-km grid spacing or less), to project an increase in the frequency of the stronger tropical cyclones

Conclusions

There seems to be a fairly broad consensus that the intensity of the largest storms will increase over the next century. However, there seems to be considerable variation in the projections for frequency between different models on one hand, and different studies on the other. The role of downscaling appears to be important to the outcomes of these studies, with models run at a higher resolution tending to project higher frequencies of storms.

Typhoon Haiyan

I woke up this morning to news of Typhoon Haiyan and its aftermath. It made for sobering listening, and hearing first hand accounts of the destruction drove home quite how massive and powerful this typhoon was, along with the effect it has had on the Philippines. The death toll has reached almost 1000 people with over 10,000 feared dead, as well as many hundreds of thousands now finding themselves without shelter, let alone food, water or electricity. The storm surge (which now seems like a far more malevolent title for this blog than when I picked it) appears to have reached over 5 metres, which is comparable to the water heights seen in the 2011 Japanese Tsunami. This "super typhoon" was a category 5 cyclone with a maximum wind speed of gusts of 235mph, and was strong enough to deposit large ships hundreds of metres inland:

It is possibly the largest typhoon to make landfall, and it's the 13th typhoon to hit the Philippines this year. The government there has set aside almost $500 billion for the rehabilitation efforts.

Possible attribution of Typhoon Haiyan to climate change?

 

Linking individual events to climate change is extremely hard. It is also a contentious issue that can bring out heated discussion. However, with climate talks starting in Warsaw at the moment, and the envoy for the Philippines vowing to fast until meaningful progress has been reached, I think it is important that these questions are asked. The same envoy, Naderev Sano, issued an emotional appeal at last year's climate talks in Doha. His words seem remarkably prescient now:



In the next few posts I will look at these questions, and see whether it makes sense to link a particular event to climate change,  whether the frequency or intensity of these events might increase due to climate change and if their effects will be more pronounced in the future.

Finally, this extreme weather event is above anything else a humanitarian crisis. Many people have lost their lives and many more will need aid in the next few months. There are a number of charities who are collecting specifically for Typhoon Haiyan. You can donate using one of the links below:

• Oxfam 
• Unicef 
• Save the Children 

Hey Jude

The St Jude day storm passed over early this morning and the devastation here was pretty horrendous:

Somewhere in a garden near Finsbury Park

It was lucky that our class on this afternoon was cancelled to give me time to repair the damage done to our garden, or at least make a start on it. Here is some more reaction to the storm and its aftermath, not for the faint hearted!

When does bad weather become Extreme Weather?

In the UK, we're used to bad weather, we get it all the time. And we love to talk about it (or so the stereotype goes). The weather is indeed... variable, perhaps making it more interesting than say the predictable weather of some of our European cousins. But our weather is actually pretty tame compared with some other part of the world. In fact, we are blessed with a moderate climate that throws up relatively few extreme weather events. This is due to a few factors: being an island and our mid-latitudes location play a big role in keeping our weather stable, and the North Atlantic Current keep winter temperatures about 10 degrees warmer than the would be if it were to 'turn off'.

We do experience some extreme weather though, sometimes a hurricane gets a little lost in the Atlantic and heads our way:

Hurricane Gordon: 2006

As an island, we also experience heat waves, droughts, floods, cold snaps, snow storms and high winds. We typically suffer a few tornadoes a year, although we have a long way to go before we reach the levels seen in tornado alley. Some of these events are clearly extreme, although we still don't have a good definition for what 'extreme weather' is.

What is Extreme Weather? 

Definition 1: outside of normal conditions

There are a few different answers depending on which definition of an extreme weather event you take. The first is that on average 5% of weather is extreme (according to the NOAA). That is, events that happen on average less than 5% of the time should be classed as extreme. Whilst this is a useful working definition, it suffers from one major drawback: the amount of extreme weather events will never increase above 5%. Clearly this is a problem if we want to look at whether these events are increasing or decreasing in frequency! So this definition works better when thinking about weather systems, as opposed to thinking about how weather events fit into the large climate systems. This definition of extreme weather does avoid seemingly nonsensical claims like "Extreme events will be the norm" by John Prescott though!

Definition 2: Outside of predefined limits

An alternative way of defining an extreme weather event, as taken from section 1.3.3 in this paper on extreme events, is to pick a value for a variable that you are monitoring, and define a maximum or minimum for that variable which is 'extreme' when averaged over a particular time period. According to the paper for example, a typical maximum value for temperature averaged over a month is 25°C. Any time that the temperature exceeds this is classed as an extreme weather event. Although the particular limit is somewhat arbitrary and will be location dependent, this has the advantage of allowing you to easily track the increase or decrease in the frequency of extreme weather events over time.

Closing remarks

All extreme weather events are interesting in their own right. However, some are not easily modellable by climate models. This is because the models are not run at a high enough resolution, either spatially or temporally, to capture the processes involved. A good example of this would be tornadoes; it is hard to capture an event that happens over ~100s of metres/half an hour if your model is running with a grid size of 10km and once per hour (although this may change!). So in the next few posts I'll be focussing on extreme weather events that are more amenable to being modelled over yearly timespans such as droughts, heat waves and cold snaps.

EDIT: Added a heading for each definition

So here it goes...

I've often thought of keeping a blog, but never quite got round to it. So here it goes...

In this blog I want to have a look at the links between climate change and extreme weather events, with a particular emphasis on the predictions climate change models make about how these events are going to unfold over the coming years and decades. But before looking into the future, I'll go back and review some of the evidence for whether the weather is changing, and if we are seeing more extreme weather events (or surges in storms to put it another way) than 100 years ago.

I'd also like to have a look out how particular extreme weather events, e.g. Hurricane Sandy, are portrayed by both the scientific community and the wider media. As noted in the IPCC SREX 2012 (PDF) report for policy makers:

Attribution of single extreme events to anthropogenic climate change is challenging.

However there seems to be a natural human tendency to look for reasons for these events, and we're probably all guilty of seeking too simplistic a reason occasionally.

This is going to be a learning experience for me, I hope it's interesting and provokes a few thoughts here and there. I'm looking forward to developing my own understanding of a fairly large and complex topic area, and sharing what I find. So stay tuned for a whistle-stop tour of extreme weather events!