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.