Greenhouse gases star in space movies
22 March 2007
Everyone agrees that our planet is getting warmer. Most scientists believe that ‘greenhouse gases’ – mainly carbon dioxide and methane - are to blame because they trap heat, stopping it from escaping into space. However, it is not easy to find out where they come from and how much is produced in different places.
One answer is to measure greenhouse gases from space. Data sent back by ESA’s Envisat spacecraft between 2003 and 2005 have now been used to map their changing distribution. The movie of carbon dioxide (CO2) shows how our planet ‘breathes’. Each year, huge amounts of the gas are taken up by growing vegetation. CO2 is then released during the autumn and winter when some of the vegetation dies and decays. Studies show that carbon dioxide levels are rising by 0.5-1 per cent each year.
The first-ever movie of methane distribution also shows levels peaking during the northern summer and falling during the winter. One surprise is that more methane than expected is released over tropical rainforests. This is important because methane is 20 times more efficient at trapping heat than CO2. Also, methane levels may rise significantly in the future if global warming melts the frozen ground in the Arctic.
Continued study of these gases by satellites is vital. At present, there are gaps in our knowledge about where the gases come from and how they are removed from the atmosphere. Space data will make it easier to predict climate change and monitor international treaties aimed at reducing greenhouse gas emissions.