Russian Heat Wave - Round 3

Following on from one post that found no evidence that a changed climate was responsible (Dole et al. 2011) for the Russian heat wave of 2010, and another that found exactly the opposite by Rahmostorf and Coumou (2011), I'm going to look at whether it's possible to reconcile the two approaches.

1000 Earths

The approach taken by Otto et al (2012) was to model the Earth's atmosphere as many times as they could, looking for the proverbial needle in the haystack. The needles they were looking for were events that were similar to the 2010 Russian heat wave, and the reason they needed so many models is because they are looking specifically for rare events, so a large number of runs of the climate is necessary to find these statistical outliers. 20 years ago, the only way to do this would have been to convince a large institution to loan you their supercomputer, nowadays an alternative exists: convince a large number of people to download and run a small program using the idle time of their computers. This is a remarkable crowd sourcing achievement, allowing people to run the HadAM3P atmospheric model on their laptops and desktops (which are about as powerful as an early 90s supercomputer by the way). 

Possible clouds over the Earth in 2090
(running on my laptop)

So how does this help work out if the 2010 Russian heat wave is attributable to climate change? The crux of it comes down to two sets of simulations, one for the Earth as it was in 1960s, and one as it was in the 2000s, each containing over 1000 individual simulations (1600 and 1200 to be precise). The occurrence of anomalous events between these two decades can then be compared:

Magnitude and expected return time of
events similar to Russian heat wave.

What the above graph shows is the frequency of events (expressed as a return time, or the average length of time you would expect between events of a given magnitude) plotted against their magnitude, in terms of the temperature of the heat wave that was modelled. It does this for two different decades, with each blue or green circle representing a particular event in the model with corresponding return time and temperature. The Russian heat wave equivalent is shown as the dot that the arrows are pointing towards. There are two important things to take from this graph. First, the return time between an event of the size of the Russian heat wave has decreased from around 100 years to 33 year from the 1960s to the 2000s (as shown by the horizontal red arrow). Second, that the magnitude of a 33 year event has increased by around 1ºC from the 1960s to the 2000s.

Tying things together

How can this help us reconcile the two different findings by Dole et al. and Rahmstorf and Coumou? Otto et al. argue convincingly that what Dole et al. found was that the movement vertically by 1ºC was inside of natural variability, and therefore should not be judged to be caused by climate change. (Note, this is looking at the magnitude of the event.) Alternatively, Rahmstorf and Coumou found that the likelihood of this event had increased (by 5 times), which is equivalent to the horizontal movement of 100 years to 33 years in return time. (looking at expected frequencies this time.) Hence to say they are contradictory is to compare apples with oranges, because they were never analysing the same thing.

All three articles were insightful, the empirical arguments of Dole et al. and the theoretical arguments of Rahmstorf and Coumou both brought a different perspective to the same problem. However, this week's article by Otto et al. ties the both of them together in a most satisfactory manner. I can only hope that the results from the simulation currently running on my computer can help contribute to science like this in the not too distant future!

Britain gets flooded, America gets attacked by the "Polar Vortex"

It sounds like Hollywood has been drafted in to write the news for America!

The extreme weather has lead to impressive pictures from around Britain, and some staggering ones from the States.

Spot the difference!

Chicago from above

This blog tends to focus on the negative aspects of these extreme events, but will anything positive come out of this weather? The Guardian seems to think so: with wind power, water supplies and wildlife all set to get a boost. Not to mention the surfers:

Surf's up off the French coast. [Photograph: Gaizka Iroz/AFP/Getty Images]

Attributing extreme weather to climate change

Can this weather be attributed to climate change? (If you've been reading this blog you should know the answer already...) No, at least not yet. Attribution is a tricky business, although there's reason to think that a warming Arctic may lead to events like these (Cohen et al. 2010). From the article:

Further, and somewhat counterintuitively, the severe cold winter weather may be attributed to boundary forcing changes consistent with an overall warming planet. A warmer atmosphere can hold more moisture and as the interior of the NH [Northern Hemisphere] continents cool in fall, this can lead to increased snowfall. And as argued here, more extensive fall snow cover contributed to the extreme negative AO [Arctic Oscillation] observed during the winter of 2009-2010.

So if anyone claims that the current weather in the States in anyway disproves that global warming is happening, you can point them towards the above article. And I wouldn't be surprised at all to see attribution studies for the current extreme events in the next 6-9 months.

2010 Russian Heat Wave - An Alternative Approach

Following this month's earlier post on the same topic, I'd like to have another look at the Russian 2010 heat wave. The previous post focussed mainly on a paper which found that there was no reason to suspect global warming was to blame for the heat wave (Dole et al., 2011). It's worth repeating one of this paper's main findings: "We conclude that the intense 2010 Russian heat wave was mainly due to natural internal atmospheric variability".

Scientific consensus?

However, there's a difference of opinion expressed by other climate scientists, who find that there was an increased likelihood of the Russian heat wave of 2010 because of global warming (Rahmstorf and Coumou, 2011). The approach they take is appealing because of its simplicity: they use straightforward arguments based on the statistics of such events and a combination of Monte Carlo simulations and analytical solutions. The conclusions they draw are not hard to understand either: if you assume there is an underlying upward trend in the time series with some random noise added to this then you would expect there to be a higher chance of observing an extreme event towards the end of the time series than if the time series were stationary (i.e. no underlying trend). A simple visual representation of this can be seen in the graph below, which shows the average global (D) and Moscow (E) temperature record over the last 100 years.

Normalised (by the s.d.) temperature records for the Earth (D) and Moscow (E)

Using this line of reasoning they find that there is an 80% chance that the 2010 Russian heat wave was caused by the underlying warming trend, and they point out that "Our results thus explicitly contradict those of Dole et al.".

They also claim that "Fig. 4 clearly shows that the warming trend after 1980 has multiplied the likelihood of a new heat record in Moscow and would have provided a strong reason to expect it before it occurred.". This is again in contrast to the Dole et al. paper, which says that it was unpredictable. I think the resolution of these two points of view is fairly easy though: the ability to predict an event is far tougher than merely expecting that an event might happen.

In a final post on this topic in the new year I'm going to see whether these two different takes on the same event can be reconciled.

EDIT:

The final post is now up, take a look here for the final instalment.

Cool Visualisation of the Earth's wind

Here's a visualisation I just came across showing the current wind speeds and directions across the Earth. According to its about page it shows global weather conditions that are "forecast by supercomputers" and "updated every three hours".  There's more information on the site's github page, the gist of which is that it pulls weather data from the National Centers for Environmental Prediction, NOAA / National Weather Service and displays it in your browser. The map below shows the wind above Britain as it is at the moment (it certainly feels pretty windy up here in Edinburgh!).

Britain on Dec. the 18th

It should work in any modern browser, so go have a look and see what you think. It'd be interesting to see how easy it is to show other types of information, e.g. snow cover, sea ice or global temperatures, using the same infrastructure. One of the key aspects of climate science is communicating results to as wide an audience as possible, and graphically rich interactive tools like this one can only help capture people's imaginations and give them a feel for what the Earth is doing.

CryoSat Turns its Hand to Measuring Storm Surges

The satellite CryoSat's main role is, as its name suggests, to measure sea ice thickness. However, the ESA have been busy repurposing its altimeter so as it can measure sea level, even close to land.  They've used this to measure the European storm surge, and validate some models in the process. It's a taste of what Sentinel-3 will offer us, another satellite that has similar instruments to CryoSat, but is focussed on measuring sea-surface topography.

Dramatic Tidal Surges Hit East Coast of UK

The recent tidal surges that have hit the East Coast highlight a couple of points: namely that the current flood defences that are in place are vital to safeguarding properties, with the authorities saying that over 800,000 properties are said to have been protected, and that predicting how these surges are going to change over the coming decades is equally important for all people that live in the affected area. Predicting how these surges will change will allow for planning of the next generation of sea defences, which will almost certainly be required with the IPCC saying that sea levels are forecast to rise by 26 to 55cm by 2100 (WGI AR5, 2013) - even with the most ambitious cuts in emissions. The effects of the surges can be seen in the following video:

Extreme Weather across the UK

The mild windiness that we had here in London was nothing compared with what was going on up and down the country: http://www.theguardian.com/uk-news/gallery/2013/dec/05/extreme-weather-in-the-uk-in-pictures

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!