Cold comfort

Clark Cross believes that the recent snowfall in the north east of the US proves that climate warming is not an issue we need to worry about ( Letters, December 22). Weather is not the same as climate, which is the average course of weather over a period of years.

Scientists know that extreme cold events have become more frequent in recent years due to a combination of global warming and the polar vortex – a large area of low pressure and cold air that hovers over the North Pole, causing extreme cold conditions. How can global warming cause more severe winters? It seems to most people to be counter- intuitive, but the science behind the reality explains all, even to those of us who are not climate scientists.

When warm air travels into the polar region, it displaces the colder air southwards. This is the situation in the US at the moment. A pocket of displaced frigid air is covering parts of the lower 48 states. I ncreasingly warmer l and temperatures in North America and northern Eurasia have allowed more heat to be transported into the Arctic stratosphere, thus destabilising the polar vortex and allowing cold air to come down into the midlatitudes of our planet.

The result is the extreme weather now being experienced in North America. We’re l iving on a warming planet and we humans have been a major contributor to this change over the past 150 years.

There are over 7.8 billion of us, but the good news for our planet is that the world’s population is expected to virtually stop growing by the end of this century, due largely to falling global fertility rates. Not a moment too soon. CAROLYN TAYLOR

Wellbank Broughty Ferry, Dundee