Weather satellites in polar orbit make approx. 14 revolutions a day around the Earth. The satellites measure atmospheric radiation at some selected frequencies, and these measurements are used daily in near real time to update the weather forecast. On a monthly basis, the same measurements are used to study long-term variations in the troposphere temperature. The troposphere extends from the Earth’s surface up to the top of the clouds, making up about 75% of the atmosphere’s mass. When you average over the entire troposphere, you get an interesting measure of the changes in global temperature.
Global temperature has a clearly rising trend, driven upwards by our emissions of greenhouse gases such as CO2, methane (CH4) and nitrous oxide (N2O). The temperature trend over the 41 years that the satellites have made such measurements is approx. 0.18 degrees per decade (the troposphere measurement series RSS-TTT is used here). Global warming has been strongest in the northern hemisphere. But the journey upwards is a jerk, where especially the alternations between El Niño and La Niña in the Pacific leave their mark.
The Pacific Ocean is currently in a cold La Niña state, and this has meant that the global temperature in the troposphere in the three-month period (Dec-Jan-Feb) that we have just left behind, has been approx. 0.3 degrees colder than a year ago.
However, we must go back a decade to find such a strong La Niña as the one we are experiencing now. Global temperature for the same three-month period was then 0.3 degrees (2010/2011) and 0.4 degrees (2011/2012) lower than this year. We thus see a significant increase in global troposphere temperature, when comparing La Niña then and now.
Trend map for the warming of the troposphere in the period 1979-2020. (Image: RSS).