People will one day get it together and dramatically reduce greenhouse gas emissions. But – not to control your daydreams too strictly here – how exactly will world temperatures react to that day? This is a question that climate science has long answered, although demons in detail have led to some confusion.
A new study led by Nanjing University, Chen Zhou, detects and exposes another devil. Research has increasingly shown that it is not only the average surface temperature of the planet that is important for the detection of warming, but also the spatial pattern of temperatures. This can be important for calculating things like the sensitivity of the climate to greenhouse gases, but in some methods of estimating how the emission emissions affect the warming, it is not taken into account.
To see a pattern
This ‘pattern effect’ of warming in different parts of the world is affecting the way the planet is returning heat to space. For example, if the warming is a little stronger in the western equatorial Pacific – it is better to produce the sun-reflecting cloud cover and release heat upwards. If you assume that global warming is happening evenly, you will miss out on the slightest compensation.
Based on previous work, the researchers calculated the influence of the pattern effect on the contemporary world by comparing historical observations with simulations of climate models of a climate before the industrial revolution. Thereafter, they tested the pattern effect numbers using satellite measurements of the total energy balance of the earth for the past few decades. With no pattern effect, the estimated accumulation of energy in the Earth’s climate is slightly higher than the satellite measurements. But if you mix the pattern effect numbers, there are predictions that fit well with the measurements, including winding from year to year.
What does this mean for a future with low emissions? One way to calculate this was to use the observed amplification of the greenhouse effect and the change of the previous temperature by humans. Based on this calculation of the Earth’s climate sensitivity, you can ask how much warming should occur as soon as greenhouse gases stop increasing. Since the climate (mainly the oceans) cannot immediately equilibrate to a stronger greenhouse effect, the temperature takes a while to fully catch up.
But where will it be once it catches up? If the pattern effect has dampened the Earth’s response in the past, there could be more warming in the pipeline – and a warmer final outcome.
Fear of commitment
Calculations of the warming to which we are already committed also critically depend on assumptions about what our future emissions will look like – a major source of confusion. The scenario used in this article is one where we reduce enough emissions to maintain current greenhouse gas concentrations. They don’t go up anymore, but neither do they. In this simple scenario, the climate system gets the chance to catch up with a new equilibrium. However, this is not a zero emission scenario, where we stop all emissions and the concentrations of greenhouse gases start to slowly decrease as the earth swallows them.
In view of this, the results show that the accountability of the pattern effect should increase dedicated warming. For concentrations stabilizing at 2020 levels, if we wait centuries until the temperature is in equilibrium, the total warming will increase from about 1.3 ° C to 2.3 ° C since the pre-industrial period. (We have heated about 1.1 ° C so far.)
An alternative version of this scenario blurs transient gases and particles; here the ultimate warming grows from 1.6 ° C to 2.8 ° C. If this very long-term view is limited to only the year 2100, the warming of 1.3 ° C to 1.8 ° C becomes the pattern effect is offset.
The exact numbers are not really here – the researchers note that using a different data set for previous ocean temperatures shrinks the differences. It is the general finding – the existence of the pattern effect implies more dedicated warming – that is possibly important. This could mean that if you really want to limit the warming to a specific target, such as 1.5 ° C or 2 ° C, you should make a mistake on the part of even lower emissions (or plan to have more CO2 later).
But it should not cause the fear that much more global warming is suddenly inevitable. A future concentration future differs from a zero-emission future, and the final temperatures only come after a long time horizon. The real contribution of the study is to address the shortcomings in some methods of calculating our dedicated heating. And we must first show a commitment to stop warming if we want one of these scenarios – or better situations – to become the future in which we can choose.
Nature Climate Change, 2020. DOI: 10.1038 / s41558-020-00955-x (About DOIs).