Is the climate warming or cooling?
Numerous websites, blogs and articles in the media have claimed that the climate is no longer warming, and is now cooling. Here we show that periods of no trend or even cooling of the globally averaged surface air temperature are found in the last 34 years of the observed record, and in climate model simulations of the 20th and 21st century forced with increasing greenhouse gases. We show that the climate over the 21st century can and likely will produce periods of a decade or two where the globally averaged surface air temperature shows no trend or even slight cooling in the presence of longer‐term warming.
(Easterling 2009) addresses this question. They examine the long term warming trend from 1975 to 2009 and find a number of periods where there is no statistically significant trend. Eg – 1977 to 1985 or 1981 to 1989 (eyeballing the graph, I might add 1987 to 1996). Figure 1: Globally averaged surface air temperature. Two periods with no statistical significant warming trends are 1977 to 1985 and 1981 to 1989. If CO2 is steadily increasing from year to year and CO2 warms the atmosphere, why isn’t the atmosphere steadily warming from year to year? The answer is natural climate variability. Effects such as the El Nino/La Nina cycle, volcanic eruptions and solar cycles are all superimposed over the long term warming trend. This is why we’ve observed several periods of cooling (or no trend at all) amidst the last 30+ years of global warming. Such periods are to be expected. So what is the likelihood of a decade of cooling during global warming? Easterling calculates the probability – both i
