Global Warming - an Overview

by Helen Willetts BBC Broadcast Meteorologist Helen Willetts explains global warming - what the problem is and how we've contributed to it. Like our day-to-day weather, climate change is a very complex subject. The media provide us with reports about global warming but it can be difficult to form an objective opinion when scientists put forward what look like opposing views. As in any scientific discipline there is a degree of uncertainty and these conflicting arguments reflect this ongoing debate. However, the consensus is that the world is warming, and a majority of scientists believe that man is contributing to that with increasing levels of carbon dioxide (CO2). Limiting CO2 emissions is so important because of its long life cycle. Carbon dioxide produced today will remain in the atmosphere for around 100 years and we are already committed to a certain level of warming. But how this will affect us in the future is difficult to quantify and the focus of research is now turning to adaptation and mitigation. All climate projections show the world will warm to some degree, but by how much depends on many factors. Despite the underlying warming trend, our weather will continue to vary from day to day and from year to year. This natural variability ensures we have cold and warm years. Our climate is the average conditions recorded over a longer period of time and it is this that, in many scientists' opinion, is changing at an unprecedented rate. When we talk about global warming, we talk about the 'greenhouse effect'. This is actually a natural and essential feature of our atmosphere, without which our planet would be uninhabitable. This process works by the principle that certain atmospheric gases (so-called greenhouse gases) allow short-wave radiation from the sun to pass through them unabsorbed, while at the same time absorbing some of the long-wave radiation which tries to escape back to space. The net result is that more heat is received from the sun than is lost back to space, keeping the Earth's surface some 30 to 35 °C warmer than it would otherwise be.