In the News: Snowstorm hits US East Coast... in October!?!

Snow fall in New York - 30/10/2011

Record levels of snow were recorded on the East Coast of the US yesterday. According to the National Weather Service, 31.4 inches fell in Jaffery New Hampshire. The storm blanketed New York city's Central Park with 3.3cm (1.3in) of snow, almost doubling an 86-year-old record set on October 30, 1925. The storm caused chaos, killing 9 people and leaving over 3 million homes without power (The full story and news video can be found here).

In trying to find some up to date information on this storm and any links to climate change I came across a blog called 'Weather Underground' which is written by meteorologist Dr. Jeff Masters. It is well worth a look and keeps up to date with all the latest notable weather events across the world.

Jeff states on his blog that the recent snows do not, by themselves, demonstrate anything about the long-term trajectory of the planet. "Climate is, by definition, a measure of decades and centuries, not months or years." But Dr. Masters also re-emphasises that government and academic studies have consistently predicted an increasing frequency of just these kinds of record-setting storms, because warmer air carries more moisture.

Floods in England Caused by Anthropogenic Greenhouse Gases

Scenes such as those in Uckfield in the above video were witnessed all across England and Wales in October and November 2000. It had been the wettest autumn since records began in 1766 - the map below outlines total rainfall and percentage increase above average for the time of year. Over 10,000 properties were flooded and the costs as a result of the damage exceeded £1bn.

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In a recent paper published in Science, a group of scientists have been attributing flood risk and anthropogenic climate change as a result of the extreme events in 2000. As mentioned in previous posts, only general explanations are usually offered for any expected increase in flooding. They usually revolve around thermodynamic arguments for precipitation extremes, an example of which can be found here.

In this recent paper a seasonal-forecast-resolution climate model was used to create two scenarios. One realistic scenario whereby actual twentieth century climate was modelled (including atmospheric pollutant concentrations) and a second hypothetical scenario to represent climatic conditions as they might have been had anthropogenic greenhouse gas emissions not occurred. Atmosphere-ocean linkages were taken into account alongside sea surface temperatures and sea ice cover. The scenarios could then be run multiple times and runoff rates could be compared between natural and anthropogenic conditions.

The study outlines that there were sequences of intense weather systems bringing heavy precipitation pulses to catchments multiple times throughout the day in Autumn 2000. This was characterised by the displacement of the North Atlantic jet stream (see image below) bringing more intense systems further into western Europe. 

This resulted in many catchments becoming saturated. Daily river runoff was examined using a simple hydrological runoff model and the climate scenarios were compared.

Image Source

The above diagram is a summary of their results, showing that the fraction of risk attributable to twentieth century greenhouse gases are significant relative to the natural conditions (without anthropogenic impact). The black line is an aggregate relative to the full natural baseline conditions.

Model Results:

In nine out of ten cases, the model results indicate that twentieth century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales by more than 20%, and in two out of three cases by more than 90%.

These results are yet another step towards providing evidence of how extreme weather events are a direct result of human anthropogenic change. But again I will give a word of caution - changes in built environment (concrete over natural environments) could have played a part in historical model simulations in recent years (affecting both run-off and return time). Furthermore, just because an event-type becomes more likely, does not meant that it will become even more likely in the future - but it does highlight the potential impact of climate change..

"It's Raining Cats and Dogs" – Briefly putting the science aside

I alluded to the phrase ‘It’s raining cats and dogs’ in my last post, but failed to display the significance of this. In the English language it is a phrase often used to describe very heavy rainfall. If you are looking for innovative scientific research, then skip on to my next post, but for a few fun facts, carry on reading!

The origin of the phrase began in the early 18^th century where in the filthy streets of 17th/18th century England, heavy rain would occasionally carry along dead animals and other debris. The animals didn't fall from the sky, but the sight of dead cats and dogs floating by in storms could well have caused the coining of this colourful phrase.

Jonathan Swift described such an event in his satirical poem 'A Description of a City Shower', first published in the 1710, and I will leave you with the words of his famous poem:

Now in contiguous Drops the Flood comes down,
Threat'ning with Deluge this devoted Town.
...
Now from all Parts the swelling Kennels flow,
And bear their Trophies with them as they go:
Filth of all Hues and Odours seem to tell
What Street they sail'd from, by their Sight and Smell.
They, as each Torrent drives, with rapid Force,
From Smithfield or St. Pulchre's shape their Course,
And in huge Confluent join'd at Snow-Hill Ridge,
Fall from the Conduit, prone to Holbourn-Bridge.
Sweeping from Butchers Stalls, Dung, Guts, and Blood,
Drown'd Puppies, stinking Sprats, all drench'd in Mud,
Dead Cats and Turnip-Tops come tumbling down the Flood.

It's Raining Cats and Dogs

“Our results provide to our knowledge the first formal identification of a human contribution to the observed intensification of extreme precipitation”.

Four scientists based at the Climate Research Division in Ontario, Canada have recently made this bold statement. They have carried out research looking at past changes in the characteristics of extreme precipitation events. For a number of years now it has been suggested that humans may have played a role through climate change in creating the increase in heavy precipitation, but as mentioned in previous posts it has always been difficult to actually prove.

In this study they used historical climate data from between 1951 and 1999, mainly focussing on the Northern Hemisphere where data is more readily available and accurate. They used observed daily observation data from over 6000 stations alongside the CMIP3 (Coupled Model Intercomparison Project) archive for model simulations.

In order to assess anthropogenic impact segments of the historical data were used in the  simulations with either:

 - Historical anthropogenic forcing (greenhouse gases, and other anthropogenic factors such    as aerosols)

- Combination of historical natural (solar and volcanic forcing) plus anthropogenic forcing

- Unforced control simulations

They looked for ‘fingerprint patterns’ in the simulation outputs, and regression coefficients that were obtained were significantly greater than zero, indicating that anthropogenic influence is readily detectable from the historical data.

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The above image displays geographical distribution of trends of extreme precipitation indices during 1951–99. A and b are Observations; C and D are model simulations with anthropogenic forcing; E and F are model simulations with anthropogenic plus natural forcing. For each pair of panels, results are shown for annual maximum daily (RX1D) and five-day (RX5D) precipitation amounts. The units used are per cent probability per year.

The paper outlines that these changes in extreme precipitation follow the Clausius-Clapeyron relationship. Whereby there is an exponential increase of atmospheric moisture with warming, as the atmosphere can hold more water at warmer temperatures.

What’s their punch line?

“Human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land periods.”

Moreover, they claim that there results may in fact be an underestimate, due to the modelling process. As a result, extreme precipitation events may strengthen more quickly than what has been projected and may have more severe impacts than estimated. Either way it would appear that we are likely to experience an increase in extreme precipitation events over the coming decades if anthropogenic impacts continue.

As a final comment of caution, it is always worth remembering that there are always uncertainties and limitations in the observed data use in studies such as these. There are also questions over missing or uncertain external forcing’s which could account for some of the difference between the observed and simulated data. Models are also never perfect and its reliability also needs to be considered. Despite these things, this paper presents a significant step in what would appear to be the right direction and should be taken as scientific fact, unless proven otherwise.

Where's the proof?

Tornado makes it way through Baca County, Colorado, May 2010. Source

In the past year the globe has witnessed devastating drought in Africa, unusual tornado clusters in south-eastern USA, and catastrophic floods in Japan and Pakistan. It has always been difficult for climate scientists to provide proof for a direct cause and effect relationship between climate change and these extreme weather events. Predictions can be made how a warming climate can affect evaporation rates over oceans and then try to create links to cloud formation, water vapour and the atmospheric cycle in order to estimate frequency of these extreme events. But it is far from an exact science.

In the past two years groups of researchers from the United States and Britain have forme a loose coalition under the name ‘ACE’ which stands for ‘Attribution of Climate-Related Events’. They are in the process of laying out plans  for a near-real-time attribution system which can assess the changing climate’s influence on weather events as soon as they happen. The paper is being presented at the World Climate Research Programme conference in Denver, Colorado at the end of next week. It will be interesting to hear the scientific communities response to this.

However, one of the major difficulties in the attribution by ACE, and why there are still sceptics about attribution techniques, is the fact that freak weather cycles such as El Niño events have been occurring long before any anthropogenic impact. Each extreme weather event will subsequently have to be analysed as to how much was influenced by anthropogenic greenhouse warming and how much by natural cycles (baseline conditions). The analysis is also dependent upon the type of extreme weather. Temperature based events such as heat waves are far more simplistic and easier to model, but for precipitation events such as droughts and floods , the models don’t just have to take into account precipitation, but soils, natural terrain and human management of rivers and wetlands. Moreover, tornadoes are caused by a balance between moist air convection and wind shear, but it is very difficult to say for certain how climate change affects this balance.

The figure below from an article in nature summarises how attribution research attempts to quantify the effects and frequency of extreme events.

The costs of extreme weather events are substantial – both in terms of livelihoods and economic costs. The death toll from the Japan tsunami in March passed 18,000, and some 40,000 people died as a result of the heat wave across Europe in 2003. Economic costs on top of the death told make a bad situation even worse. The World Bank has estimated that it could cost Japan as much as £145bn to repair the damage from the 2011 tsunami.

As a result the global community should be ever more concerned about whether anthropogenic changes are the direct cause of these extreme events. At a very basic level you could say that humans are killing thousands of people as a result of anthropogenic warming. If these climate models and projects as put forward by ACE can help provide proof of direct links, they may help to provide some form mitigation by outlining the direct quantitative impact humans are having. It could also lead to a greater willingness for the global community to reduce greenhouse gas emissions, and give greater weight to policy decisions on the national and global scale.

Defining Extremes - FAQs

In order to explore the subject of extreme weather and climate change, there's acouple of FAQ's that I need to clarify. If you have any further burning questions, please comment and I will follow them up in future posts.

What justifies a weather event to be regarded as extreme?

In short, a weather event can be described as extreme when it lies far beyond (on either side) of the mean and median of that weather event. The easiest way to address this question is using statistics with the aid of some simple graphs:

Any event or climate variable (such as temperature or precipitation) can be described in terms of its distribution, and the solid central curve in graph (a) could represent the the present day frequency distribution of this. Shading indicates the extreme parts of the distribution (events which occur infrequently, that are far from the mean or median value).

If there is a shift of the distribution in a future climate, there will be an increase in extreme events on one end, and a decrease at the other (a). For example, if the temperature at a certain location warms by an x amount, this will almost certainly produce an increase in the number of extreme hot days and a decrease in the number of extreme cold days. It is also important to note that there is a non-linear relationship between change in mean of the distribution and extreme changes. A small change in mean can result in a large change in the frequency of extremes (Read this paper for more info on this).

The standard deviation in a future climate may change, producing changes in extreme events at both ends of the frequency distribution (b). A change in variance of a distribution has a larger effect on the frequency of extremes than a change in the mean (but has to be more than one standard deviation from the mean in order to be extreme and hold true). For example a 1 degree Celsius change in the standard deviation of the distribution will have a larger impact on the extremes than a 1 degree change in the mean of the distribution. A good paper explaining this further can be found here.

To complicate things further, you can end up with something such as that in graph (c), whereby both the mean and variance change, altering the occurrence of extremes in several ways. An example of this would be precipitation, which is not normally distributed, and a change in mean also causes a change in variance. 

Are the effects of extreme weather always negative?

No, although the negatives tend to far outweigh the positives. Despite extreme weather events often being associated with negative effects on society and the natural environment, through events such as storms, droughts, extreme colds and floods, there are also some advantages. For example, energy production and reduction in energy costs (e.g. from power generated through wind turbines in windier conditions), surplus of water in some areas of Australia (following cyclones), which feeds longer term storage. Arctic, Antarctic and Siberia may experience more plant growth and greater biodiversity with a warming climate. Also, changes in precipitation patterns may result in longer growing seasons in some areas. However, with each of these positives come many negatives, including loss of power, damage to infrastructure, reduction of growing seasons, loss of biodiversity... the list goes on.

As a short and sweet introductory reading to this subject, I can suggest this free-to-access paper which gives a general overview of trends in extreme weather and climate events. It also touches upon the effects of such changes on the human and natural environment.

Coincidence or Causality?

New to the blogging world, I will keep my fist post short and sweet, a flavour of what's to come, if you will.Why start my blog with this video? Well, quite simply because it is a video that answers absolutely nothing. 

The video does however make you think by asking a lot of questions. After personally experiencing a blistering, record breaking 29.4 degrees Celsius in the UK on the 2nd October, it is not uncommon to create a logical connection between climate change and these extreme weather conditions. Is there a much bigger link to it all, or are they just freak anomalies? 

This blog will flirt around with thoughts, news stories and academic debates in an attempt to answer questions surrounding extreme weather conditions and climate change. What lies ahead in the future? Are there any indicators of similar patterns of extreme weather events in the past? Or is this all just one big coincidence? 

“There have been tornadoes before, and floods — that’s the important thing. Just be careful to make sure you don’t let yourself wonder why all these record-breaking events are happening in such proximity — that is, why there have been unprecedented megafloods in Australia, New Zealand and Pakistan in the past year. Why it’s just now that the Arctic has melted for the first time in thousands of years. No, better to focus on the immediate casualties, watch the videotape from the store cameras as the shelves are blown over…” Bill McKibben 350.org

So I will leave you with this initial thought to ponder, are extreme weather events and climate change coincidence or is there some form of causality?