Extreme weather and climate change
The UK is coping with the aftermath of a series of storms from the Atlantic and hoping for some respite from an abnormally wet winter. A coastal stretch of one of the main train lines to the South West was left hanging in mid-air, tens of thousands of homes have been without electricity at various times, flood-prone areas such as the low-lying Somerset levels have been completely inundated and many communities along the Thames west of London have experienced much greater flooding than most residents have ever seen. Apart from rivers overflowing, the saturated earth means the water table is above ground in many places in the South.
The British Isles may have borne much of the brunt of this exceptional weather, but other countries in Western Europe (Spain for example) have also had much higher than average rainfall. Meanwhile, every US state other than Florida had snow on the ground at the end of last week, and this snowfall had been preceded by bitter cold across Canada and America. Tokyo also has had a record amount of snow, while Australia and Brazil have suffered heatwaves and drought.
It is human nature to wonder what is behind these patterns of extreme weather, some of which may be worse than we have previously experienced in our own lifetimes. But the weather is capricious and, while new records are set almost daily somewhere in the world, similarly extreme patterns may often be found in historical records. Whether or not the recent patterns have been uniquely bad depends to a large extent on the period of time considered.
In the comparatively recent past – certainly within the lifetimes of many – there has been the exceptionally cold winter of 1946/7, followed by an extremely hot summer. 1953 saw disastrous floods in eastern England and parts of the Netherlands. A decade later, the winter of 1962/3 will be remembered for heavy snow, which lay for weeks in an extended period of sub-zero temperatures (January was the coldest month of the century and the coldest since January 1814). 1976 was a drought year, with reservoirs in England drying up and many people reliant on standpipes for water. Two years later, the weather was cold enough to prevent diesel engines starting, in the worst winter since 1963. In 2003, much of Europe suffered an intense heatwave under a stationary high pressure system.
These are just a few of the regional events many of us have experienced. Extreme weather is nothing new, although it often continues to surprise us. The big question at present is whether it is becoming even more extreme or more common. The reason this is more than usually important is that storms, floods and droughts have all been projected to become more common as global temperatures rise. There are people in the climate change community who look to such changes to reinforce their case that global warming is a real threat.
The problem is to agree just what constitutes an increasing frequency. Because weather systems are intrinsically chaotic, most patterns are often difficult to discern. In some cases, however, there is a regular season and a long series of records, for example for north Atlantic hurricanes. Some mainstream climate scientists had predicted that there would be more hurricanes as surface waters warmed and more energy was transferred to the atmosphere. In fact, the last few seasons have been rather quiet, and there has been no increase in the intensity of storms.
Neither has there been any increase in the overall number of tropical storms (Atlantic hurricanes and Pacific typhoons). Typhoon Haiyan, which hit parts of Southeast Asia in 2013 (and killed over 6,000 people in the Philippines), was an exceptionally severe storm which was still at full strength when it first made landfall. Record wind speeds were measured over land, surpassing Hurricane Camille in 1969, but no record was set for low pressure at the heart of the storm. Observations in the Pacific show a relatively low level of tropical cyclones since the mid-1980s, with individual years strongly influenced by El Niño events (Tropical cyclone trends).
Rainfall patterns may have been out of the ordinary for Western Europe recently, but heavy rains during the Asian monsoon season are the norm and are vital in providing water after the dry season. Failure of the rains can be catastrophic, but so can an exceptionally wet season, and there have been suggestions that global warming could alter the pattern of monsoons.
However, scientists in the University of California San Diego have found there is a physical coupling between weather patterns in the western Pacific and Indian Ocean. In particular, one year’s monsoon appears to be strongly influenced by El Niño events the previous summer (Asian monsoon is getting predictable: Strong correlation between summer monsoon and preceding climate pattern). There seem, at least in this case, to be factors other than global temperature at work.
Unfortunately, some people have used recent floods, storms and heatwaves as evidence of what climate change might bring, while often trying not to blame global warming directly for particular events. It seems to be a matter of guilt by association, brought on by a deep conviction that climate change presents real threats and that the public support for action can be boosted in this way.
Quite recently we read that David Cameron ‘very much suspects’ climate change is behind recent storms. Politicians often have to say what is expedient, and the Prime Minister may have thought he had no choice but we might hope that senior scientists would be rather more careful. Not so Dame Julia Slingo, UK Met Office chief scientist, as reported by the BBC – Met Office: Evidence ‘suggests climate change link to storms’.
However, this must be seen as a personal opinion rather than based on evidence, despite Dame Julia’s claim that ‘…all the evidence suggests there is a link to climate change’. Her statement is at odds with the more measured statements in the latest IPCC Assessment Report.
Overall, the impression is that some people are taking whatever opportunities they see to find examples of what global warming may be doing, which by inference is then due to our carbon dioxide emissions. The purpose is presumably to stiffen political backbones and keep policies aimed at radical decarbonisation on track. However, there is as much chance that many members of the public will see such statements either as overreaction or simply irrelevant.
When hit by storms, flood or drought, people look to governments to help them recover and hopefully avoid a similar situation in future. Canny politicians will realise that the balance of climate change policy must swing much further towards adaptation rather than mitigation if voters are not to become increasingly alienated. Cutting carbon dioxide emissions might make a modest difference to what happens in fifty years but, in the meantime, low-lying areas, coastlines and riverbanks remain vulnerable to flooding and other damage.