A new study, just published in Environmental Research Letters by Steven Sherwood and Nidhi Nashant, has answered a number of questions about the rate at which the Earth is warming. Once again, the mainstream science regarding warming of the atmosphere is shown to be correct. This new study also helps to answer a debate amongst a number of scientists about temperature variations throughout different parts of the atmosphere.
When someone says “The Earth is warming”, the first questions to ask are (1) what parts of the Earth? and (2) over what time period? The Earth’s climate system is large; it includes oceans, the atmosphere, land surface, ice areas, etc.
When scientists use the phrase “global warming” they are often talking about increases to the amount of energy stored in oceans or increases to the temperature of the atmosphere closest to the ground. By either of these measures, climate change has led to a progressive increase in temperatures over the past four decades. But what about other parts of the climate system? What is happening to them?
One important area to consider is the troposphere. It is the bottom portion of the atmosphere where most weather occurs. Tropospheric temperatures can be taken by satellites, by weather balloons, or other instruments. In the past, both satellites and weather balloons reported no warming or even a cooling.
However, that original work was shown to be faulty and now even the most strident sceptics admit that the troposphere is warming. But obtaining an accurate estimate of the rate of warming is difficult. Changes to instruments, errors in measurements, short term fluctuations all can conspire to hide the “real” temperature.
This is where the new study comes in. The authors develop a new method to account for natural variability, long-term trends, and instruments in the temperature measurement. They make three conclusions.
First, warming of the atmosphere in the tropical regions of the globe hasn’t changed much since the late 1950s. Temperatures have increased smoothly and follow what is called the moist-adiabatic rate (temperature decrease of humid air with elevation). This result is in very close agreement with climate computer models and it contradicts the view that there is a slowdown in climate change.
Second, the vertical height of the tropics that has warmed is a bit smaller than the models predict. Finally, there is a change in observed cooling in the stratosphere – the layer of the atmosphere above the troposphere.
Taken together, these results show that the tropospheric warming has continued as predicted by scientists years ago.
Embedded in this research is a conclusion about the so-called “tropospheric hot spot”. This “hot spot” refers to expectations that as global warming progresses, the troposphere will warm faster than the Earth surface. The hot spot is really hard to detect; it requires high quality measurements at both the surface and throughout the troposphere. Past studies which could not detect a hot spot were often used by climate contrarians to call into question our simulation models and even our basic understanding of the atmosphere.
But this new study finds a clear signal of the hotspot. In fact, the temperature in the troposphere is rising roughly 80% faster than the temperature at the Earth’s surface (within the tropics region). This finding agrees very well with climate models which predicted a 64% difference.
And this is exactly how models are supposed to work. Models can be used to predict changes that will occur in the future. Once we make measurements, we can compare them with the models. If the two disagree, it either means our models are wrong, our measurements are wrong, or both are wrong. More often than not, the models have been found to be vindicated.
In the case of the tropospheric temperatures, initially the models and experiments disagreed. Both were rechecked and scientists found the experiments were misinterpreted. When improved experiments were obtained, we see atmosphere temperature studies in agreement.
This study also helps us see that the troposphere is warming as we expected. Furthermore, this is yet another study that calls into question the significance ofthe so-called “hiatus.” I am hopeful that more studies on this important topic will be completed in the near future. Measurements of the Earth’s climate system and their comparison against climate models provide excellent test cases for scientists to improve their understanding of the processes that drive today’s and tomorrow’s climate.