The weather belongs on the evening news
Q: If we're so worried about global warming why has it been so cold here in the U.S., in Europe and other parts of the globe? What do weather statistics say has happened during the past 50 years? And how does weather differ from climate (is there a difference)?
At times of weather extremes, both hot and cold, windy or wet, the issue of climate change seems to come up. At the moment, with large swathes of the Northern Hemisphere experiencing bitterly cold temperatures and heavy snowfalls the question comes up again -- how can a warming world experience such weather? Therein lies the issue -- short term weather phenomena is not the same as long term climate change. In fact the way scientists model long term climate change bears little resemblance to the way others forecast short term weather, yet many will point to a failing in the latter to criticize the findings of the former. Models for short term weather forecasting are highly dependent on the input data for the start of the period -- i.e. what are the conditions I can see right now. Multi-decadal climate forecasts are not very sensitive to the initial conditions and they do not include data assimilation, so they are not expected to simulate the exact sequence of historical, let alone future, weather events.
Whilst the two must be linked, many other short lived changes drive the day to day weather. For example, this particularly cold winter also coincides with a deep minimum in the regular solar irradiance cycle, but equally the solar minimum existed last year as well and the winter in Europe was relatively mild. Or was it? We tend to remember the events that affect us directly and have little appreciation of the global picture, which is what climate change is really all about. Take December as an example -- whilst a deep cold area persisted over parts of North America and Russia, the Canadian Arctic, the seas north of Norway and parts of eastern Russia were experiencing temperatures many degrees above normal. Of course the evening news reported none of this, largely because almost nobody lives in these regions. Rather, the news readers did their job and reported local conditions for their viewers. As rising CO2 levels in the atmosphere warm the overall climate, we should also see rising levels of moisture in the air. Under the right circumstances, this can lead to much heavier snowfall than might otherwise have been the case. Heavy snowfall leaves people with the perception of a much harsher winter than normal.
Weather refers to the state of the atmosphere at a given time. It is highly variable due to the chaotic nature of the atmosphere over small time and space scales. Climate is often defined as the average weather. It is usually described in terms of the mean and variability of metrics such as temperature and precipitation over periods such as 30 years. There is no doubt that in parts of the world this is a cold winter, but equally there is no doubt that the world has warmed over the past half century.
Posted by: ignoranceisbliss | January 15, 2010 12:46 PM
Report Offensive Comment
Posted by: edbyronadams | January 15, 2010 9:12 AM
Report Offensive Comment