Climate Change Effects

Climate Change Effects

Despite the US government previously asserting Climate Change was not something which was actually happening, the general consensus worldwide is now that global warming is a fact. As a result, the risk of flash flooding has increased due to a rise in the mean sea level and an increase in the incidence of extreme weather events are also now being recorded.

Since its completion in October 1982, the number of times each year that the Thames Barrier has been closed has been steadily increasing and it is projected that within the next 20 years the barrier will no longer be effective at preventing the highest storm surges from travelling up the Thames beyond Greenwich.

Polar and Glacial Ice Melt – Rise in Sea Levels

According to the Intergovernmental Panel on Climate Change’s (IPCC) Second Assessment on Climate Change 1995, the global sea level has risen between 10 and 25 cm in the past 100 years and much of the rise may be related to the increase in global mean temperature. The average sea level is projected to rise, mainly due to the thermal expansion of the oceans and the melting of glaciers and ice-sheets, 50 to 95 cm by 2100 and will continue to rise at the same rate beyond 2100, even if the concentrations of greenhouse gases and global mean temperatures are stabilised by that time.

In London and the Southeast, the rise in the mean sea level has been of the order of 60 cm in the last century. This increase is in part due to the tilting of the British Isles (with the south eastern corner tipping downwards) and the settlement of London on its bed of clay.

In common with the Thames Barrier most current sea defences will be ineffective against the increase size of storm surges, caused by a combination of higher sea levels and more violent storms. Properties protected by these defences can expect to be flooded annually.

Extreme Weather Events

The UK's historically moderate climate – not too hot, cold, wet or dry is now changing. Worldwide, the proportion of hurricanes reaching categories 4 or 5 – with wind speeds above 56 metres per second – has risen from 20% in the 1970s to 35% in the 1990s. Cyclones pick up energy over warm water and as sea temperatures rise the violence of cyclones reaching the UK will increase. These storms have higher wind speeds and deliver more precipitation and thus increase the chance of flooding from storm surge, river inundation and flash floods.

Increased extreme weather means that rain is more likely to fall on ground hardened by a long hot, dry period especially in the summer and unable to absorb it - leading to flash floods instead of a replenishment of soil moisture or groundwater levels

Failure of the Gulf Stream

The Gulf Stream, together with its northern extension, the North Atlantic Drift, is a powerful, warm, and swift Atlantic thermohaline ocean current that originates in the Gulf of Mexico, exits through the Strait of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean. At about 30°W, 40°N, it splits in two, with the northern stream crossing to northern Europe and the southern stream recirculating off West Africa.

Its extension toward Europe, called the North Atlantic Drift, makes Western Europe and especially Northern European winters warmer than they otherwise would be by approximately five degrees Centigrade. Average monthly temperatures in Røst and Værøy in Lofoten, Norway, never drop below freezing in winter even though they are inside the arctic circle.

There is some speculation that global warming could decrease or shutdown thermohaline circulation and therefore reduce the North Atlantic Drift. This could trigger localised cooling in the North Atlantic and lead to cooling, or lesser warming, in that region affecting in particular areas like the UK that are warmed by the North Atlantic Drift. The chances of this occurring are unclear.

At present, available data shows the Gulf Stream flow was stable over the past 40 years, although there is evidence that the deep return flow is weakening (according to one study even by 30% since 1957), which would imply a weakening in the North Atlantic Deep Water production. However, this should cause a temperature drop of a few degrees in North West Europe, which has not been observed. At least part of the apparent weakening of the Gulf Stream (if real) may be cyclical and connected to recent positive values of North Atlantic Oscillation. (The Climatic Research Unit has a detailed explanation of the North Atlantic Oscillation.)

A thermohaline circulation shutdown could have other major consequences apart from the cooling of Europe such as an increase in major floods and storms, the collapse of plankton stocks and the consequential impact on fish and marine mammals.

Other Effects

The optimists have hailed global warming as a chance to increase agricultural production, and barley is now a significant crop in Iceland whereas it was impossible to grow this crop 20 years ago.

It seems likely that melting Arctic ice may open the Northwest Passage in summer, which would cut 5,000 nautical miles from shipping routes between Europe and Asia. This would be of particular relevance for supertankers which are too big to fit through the Panama Canal, but the melting of the sea ice is also likely to make the polar bear that does not hunt on land extinct in the near future.

We have already seen the spread northwards of many species, but amongst the delights of new butterfly species, exotic fish in our seas and Little Egrets in our estuaries come some less than welcome immigrants such as malaria and other tropical deseases that are likely to establish themselves in the UK.

Useful Links

Thames Barrier information from the Environment Agency focusing on its construction and current operation, in addition to it being understandably silent on its effectiveness in the future: Thames Barrier Information

Intergovernmental Panel on Climate Change (IPCC): http://www.ipcc.ch

The BBC Weather Centre daily weather forecasts

The Met office information about the UK climate and weather statistics

UK Climate Change Programme What is the government doing?

Ocean and Climate Change Institute part of Woods Hole Oceanographic Institute: Understanding the role of the ocean on the global climate

Articles of Interest

National Oceanography Centre at Southampton University. Latest news articles