Swiss weather researcher Kerstin Treydte and colleagues say they discovered that the last century saw the biggest increase in snowfall in central Asia than at any time over the previous millennium.

The precipitation started to surge around 150 years ago, coinciding with the start of the Industrial Revolution powered by coal, gas and oil -- the biggest culprits for greenhouse gases.

Scientists say they have accumulated solid evidence that global warming is accelerating and may already be affecting the world's climate system, although many key questions remain to be answered.

One of them is how warming may affect rainfall and snowfall patterns. This is difficult to establish over a long period, given that accurate measurements date back at best to a century and a half and for a long time were only carried out in industrialised countries.

Treydte's team took a new approach, looking for levels of oxygen isotopes found in water molecules trapped in tree rings in northern Pakistan. More precipitation leads to lower concentrations of the heaviest isotope.

The trees studied were junipers that grew in the Karakorum and Himalayan mountains, which surround the upper reaches of the Indus Valley.

Meanwhile, another paper suggests that some corals may be better able than previously thought to survive so-called bleaching.

Some experts fear that rising sea temperatures could cause 60 percent of Earth's coral reefs to be bleached over the next few decades.

Bleaching occurs when a stressed coral expels the microscopic algae that inhabit it, provide it with nutrients in exchange for a home and coincidentally give it its colour.

Without these plant cells, only the white, calcium-rich coral skeleton is left and if the bleaching is prolonged, the coral will eventually die.

Ohio State University researcher Andrea Grottoli grew rice coral (Montipora capitata) in a tank and warmed up the water to cause bleaching.

The coral was still able to meet its energy needs by preying on zooplankton -- minute animals that float around on the sea and in the reefs.

But two other tested coral varieties, finger coral (Porites compressa) and lobe coral (P. lobata), were unable to adapt as they depended entirely on symbiotic algae for their nutrients.

This suggests that coral ecosystems may not be wiped out by global warming but will still undergo wrenching change because more resilient species will dominate the reefs, say the authors.

The two studies appear on Thursday in Nature, the weekly British science journal.

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