Evidence For Climate Change

by John Cook

In November, the servers at the University of East Anglia in Britain were illegally hacked and emails were stolen. When a selection of emails between climate scientists were published on the internet, a few suggestive quotes were seized upon by many claiming global warming was all just a conspiracy. Set aside for a moment the fact that the most cited emails were quoted out of context or interpreted without an understanding of the science involved. An important point to realise is that the emails involve a handful of scientists discussing a few pieces of climate data. Even without this data, there is still an overwhelming and consistent body of evidence, painstakingly compiled by independent scientific teams from institutions across the world.

What do they find? The planet is steadily accumulating heat. When you add up all the heat building in the oceans, land and atmosphere plus the energy required to melt glaciers and ice sheets, the planet has been accumulating heat at a rate of 190,260 Gigawatts over the past 40 years. Considering a typical nuclear power plant has an output of 1 Gigawatt, imagine over 190,000 power plants pouring their energy output directly into heating our land and oceans, melting ice and warming the air.

This build-up of heat is causing ice loss across the globe, from the Arctic to the Antarctic. Both Greenland and Antarctica are losing ice at an accelerated rate. Even East Antarctica, previously thought to be too cold and stable, is now losing ice mass. Glacier shrinkage is accelerating. Arctic sea ice has fallen so sharply, observations exceed even the IPCC worst case scenario. The combination of warming oceans (causing thermal expansion) and melting ice has resulted in sea level rise tracking the upper limit of IPCC predictions.

There are many other physical signs of widespread warming. The distribution of tree lines, plants and many species of animals are moving into cooler regions towards the poles. As the onset of spring is happening earlier each year, animal and plant species are responding to the shift in seasons. Scientists observe that frog breeding, bird nesting, flowering and migration patterns are all occurring earlier in the year. The height of the tropopause, a layer in our atmosphere, is rising. Arctic permafrost, covering about 25% of Northern Hemisphere land, is warming and degrading. The tropical belt is widening. These results are all consistent with global warming.

What’s causing this heat build-up? Humans are emitting huge amounts of carbon dioxide into the atmosphere (29 billion tons per year). Greenhouse theory predicts that more carbon dioxide in the atmosphere will trap heat energy at certain wavelengths as it escapes out to space. What do we observe? Satellites over the past 40 years find less heat escaping to space at these wavelengths. Where does the heat go? Surface measurements find more heat returning back to the Earth's surface. Tellingly, the increase occurs at these same wavelengths. This is the human fingerprint in global warming.

There are multiple lines of empirical evidence that global warming is happening and human activity is the cause. A few suggestive emails may serve as a useful distraction for those wishing to avoid the physical realities of climate change. But they have no impact on the scientific case for man-made global warming.

John Cook, a physicist, focuses on the science of climate change at his website, skepticalscience.com.