Climate change: 20th century the wettest in Pakistan for 1,000 years

Since the beginning of industrialisation the amount of precipitation in Pakistan has increased considerably. This is shown by what is the first evaluation worldwide of isotopes in the annual rings of juniper trees which are more than 1,000 years old.

In the forthcoming issue of the journal Nature on 27 April, scientists from the Swiss Research Institute WSL, the Potsdam Geo Research Centre, the Jülich Research Centre and the University of Bonn report that these show that the 20th century was the wettest century in the past millennium in northern Pakistan. The reason could be global warming: when the temperature rises, the atmosphere can store more humidity, which in turn results in more snow and rain falling. The increase in precipitation is unprecedented, at least for the last 1,000 years. The researchers therefore conclude that human influence is not unlikely.

Annual rings are sensitive indicators of the climatic and environmental conditions in which they grow. ‘If trees become stressed – for example in particularly dry years – their trunk growth is less than in good times,’ Professor Matthias Winiger, of Bonn’s
Geographical Institute, says. ‘The annual rings then tend to be correspondingly close together.’ The analysis of the oxygen absorbed by the wood is even more revealing. For this the ratio of two varieties of oxygen which differ in weight, what are known as isotopes, is measured. ‘This method is extremely complex, but permits very exact statements to be made about the humidity conditions in the year in question,’ Professor Winiger explains.

The team of scientists examined four stocks of trees in the Karakorum Mountains and the Himalayas. Juniper trees can live to a ripe old age. In one of the stocks of trees the annual rings could be followed back to 828 A.D. Their wood is thus a very reliable ‘climate archive’ going back more than 1,000 years. In order to estimate the accuracy of the data, the researchers compared the precipitation graphs based on the annual rings over a reference period with observation data from meteorological stations. However, these have only been available in the mountains of Pakistan since 1898. ‘For this period of time our method tallies remarkably well with the meteorological data,’ Professor Winiger emphasises.

The results show that there must have been particularly wet periods in the past, too, e.g. around 1200 or 1350. However, in the late 19th and the whole of the 20th centuries such ‘precipitation peaks’ were both especially high and remarkably frequent. The development of precipitation in Pakistan thereby shows parallels with the global rise in temperature which has been observable over the past 150 years. Among other effects it influences atmospheric processes, particularly what is known as the atmospheric circulation. By this scientists mean the global air currents which are primarily driven by the warmth irradiated by the sun.

It is presumed that climate change can at least in part be traced back to the green-house gases such as carbon dioxide and steam, which are produced directly or indirectly by human beings. The authors of the study reveal that they are themselves concerned about their findings: they write that ‘in these sub-tropical and peripheral tropical regions changes in the precipitation rate and distribution and thus in the water balance would have a much greater impact on people’s well-being and changes in the eco-systems than the change in temperature on its own.’

Source: University of Bonn

Related stories:

Climate change caused widespread tree death in California mountain range
Warmer temperatures and longer dry spells have killed thousands of trees and shrubs in a Southern California mountain range, pushing the plants' habitat an average of 213 feet up the mountain over the past 30 years, a UC Irvine study has determined.
Climate change and species distributions
Scientists have long pointed to physical changes in the Earth and its atmosphere, such as melting polar ice caps, sea level rise and violent storms, as indicators of global climate change. But changes in climate can wreak havoc in more subtle ways, such as the loss of habitat for plant and animal species. In a series of talks at the Ecological Society of America (ESA) 93rd Annual Meeting, climate change scientists will discuss how temperature-induced habitat loss can spell disaster for many living things.
Climate change goes underground
Climate change, a recent “hot topic” when studying the atmosphere, oceans, and Earth’s surface; however, the study of another important factor to this global phenomenon is still very much “underground.” Few scientists are looking deep enough to see the possible effects of climate change on groundwater systems. Little is known about how soil, subsurface waters, and groundwater are responding to climate change.
MIT tool determines landslide risk in tropics
Engineers at MIT have devised a simple yet effective system for determining an area's landslide risk, a tool that could help planners improve building codes, determine zoning and strengthen mitigation measures in mountainous tropical regions frequently hit by typhoons.
'Build parks to climate proof our cities'
Scientists looking at the effect global warming will have on our major cities say a modest increase in the number of urban parks and street trees could offset decades of predicted temperature rises.
Annual plants may cope with global warming better than long-living species
Countering Charles Darwin's view that evolution occurs gradually, UC Irvine scientists have discovered that plants with short life cycles can evolutionally adapt in just a few years to climate change.
How trees manage water in arid environments
Water scarcity is slowly becoming a fact of life in increasingly large areas. The summer of 2006 was the second warmest in the continental United States since records began in 1895, according to the National Climatic Data Center. Moderate to extreme drought conditions were evident in about 40 percent of the country.
Researchers say rise in California temperatures likely to affect crops
Increasing temperatures in California during the next 45 years could negatively affect the amount of almonds, walnuts, oranges, avocados and table grapes that Americans put on their tables. According to new research in the journal Agricultural and Forest Meteorology, production losses in some of California’s most popular crops could be as high as 40 percent by mid-century.

News discussion:

Space & Earth science news