Q: Are the weather patterns of the planet changing, if so, how?

Richard, Grade 12

Portsmouth, Hampshire, England

A: Our perspective is that in the atmospheric science community there is general agreement that global surface temperatures are increasing, by about 1 degree Kelvin to date starting from the early 1900s as the baseline. Moreover, two sets of satellite measurements of temperatures way up in the atmosphere also demonstrate a warming, although one of the two sets of satellite measurements is not conclusive on this point at this time. Regionally, there is agreement that glaciers are melting a bit and retreating everywhere, particularly in the tropics. (Some scientists believe that the vanishing tropical glaciers are like "canaries in coal mines" because they signal a dramatic change to a warmer global climate.)

Moreover, temperatures in the Arctic, for example Alaska, have risen significantly -- we seem to recall a study that indicates that annual average temperatures in Alaska are up by about 5 Kelvin. While many scientists support the contention that these changes are due to global warming, other scientists do not rule out the possibility that natural variability in the sun, the orbit of the earth, and internal dynamics of the earth is an important source of these changes as well.

If temperatures go up a bit, then there will be more evaporation of water from the world's oceans. The argument then goes that the energy associated with the evaporated water will lead to stronger hurricanes, mid-latitude storms and stronger atmospheric weather patterns in general. As weather patterns strengthen, so too will the regional weather associated with them: stronger rain and snow storms and stronger associated draughts and dry spells. For example, some scientists believe that there is a link between the increase in global temperatures and the frequency of El Nino and La Nina. Strong episodes of El Nino and La Nina are usually linked to dramatic shifts in hemispheric weather patterns, and any change in their frequency will likely have rippling effects.

However, the weather, as we know, is quite variable in the first place and varies naturally on scales from days to weeks to months to years to decades to centuries to millennia. Actually detecting changes in the weather patterns becomes, as a result, a tricky business and figuring out the cause of those changes is even more difficult.