At a glance - How sensitive is our climate?

On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "How sensitive is our climate?". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.

Fact Myth Mars

At a glance

Climate sensitivity is of the utmost importance. Why? Because it is the factor that determines how much the planet will warm up due to our greenhouse gas emissions. The first calculation of climate sensitivity was done by Swedish scientist Svante Arrhenius in 1896. He worked out that a doubling of the concentration of CO2 in air would cause a warming of 4-6oC. However, CO2 emissions at the time were miniscule compared to today's. Arrhenius could not have foreseen the 44,250,000,000 tons we emitted in 2019 alone, through energy/industry plus land use change, according to the IPCC Sixth Assessment Report (AR6) of 2022.

Our CO2 emissions build up in our atmosphere trapping more heat, but the effect is not instant. Temperatures take some time to fully respond. All natural systems always head towards physical equilibrium but that takes time. The absolute climate sensitivity value is therefore termed 'equilibrium climate sensitivity' to emphasise this.

Climate sensitivity has always been expressed as a range. The latest estimate, according to AR6, has a 'very likely' range of 2-5oC. Narrowing it down even further is difficult for a number of reasons. Let's look at some of them.

To understand the future, we need to look at what has already happened on Earth. For that, we have the observational data going back to just before Arrhenius' time and we also have the geological record, something we understand in ever more detail.

For the future, we also need to take feedbacks into account. Feedbacks are the responses of other parts of the climate system to rising temperatures. For example, as the world warms up. more water vapour enters the atmosphere due to enhanced evaporation. Since water vapour is a potent greenhouse gas, that pushes the system further in the warming direction. We know that happens, not only from basic physics but because we can see it happening. Some other feedbacks happen at a slower pace, such as CO2 and methane release as permafrost melts. We know that's happening, but we've yet to get a full handle on it.

Other factors serve to speed up or slow down the rate of warming from year to year. The El Nino-La Nina Southern Oscillation, an irregular cycle that raises or lowers global temperatures, is one well-known example. Significant volcanic activity occurs on an irregular basis but can sometimes have major impacts. A very large explosive eruption can load the atmosphere with aerosols such as tiny droplets of sulphuric acid and these have a cooling effect, albeit only for a few years.

These examples alone show why climate change is always discussed in multi-decadal terms. When you stand back from all that noise and look at the bigger picture, the trend-line is relentlessly heading upwards. Since 1880, global temperatures have already gone up by more than 1oC - almost 2oF, thus making a mockery of the 2010 Monckton quote in the orange box above.

That amount of temperature rise in just over a century suggests that the climate is highly sensitive to human CO2 emissions. So far, we have increased the atmospheric concentration of CO2 by 50%, from 280 to 420 ppm, since 1880. Furthermore, since 1981, temperature has risen by around 0.18oC per decade. So we're bearing down on the IPCC 'very likely' range of 2-5oC with a vengeance.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!


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In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:

Myths with link to rebuttal Short URLs
Ice age predicted in the 1970s sks.to/1970s
It hasn't warmed since 1998 sks.to/1998
Antarctica is gaining ice sks.to/antarctica
CRU emails suggest conspiracy sks.to/climategate
What evidence is there for the hockey stick sks.to/hockey
CO2 lags temperature sks.to/lag
Climate's changed before sks.to/past
It's the sun sks.to/sun
Temperature records are unreliable sks.to/temp
The greenhouse effect and the 2nd law of thermodynamics sks.to/thermo
We're heading into an ice age sks.to/iceage
Positives and negatives of global warming sks.to/impacts
Global cooling - Is global warming still happening? sks.to/cooling
How reliable are climate models? sks.to/model
Can animals and plants adapt to global warming? sks.to/species
What's the link between cosmic rays and climate change? sks.to/cosmic
Is Al Gore's An Inconvenient Truth accurate? sks.to/gore
Are glaciers growing or retreating? sks.to/glacier
Ocean acidification: global warming's evil twin sks.to/acid
The human fingerprint in global warming sks.to/agw
Empirical evidence that humans are causing global warming sks.to/evidence
How do we know more CO2 is causing warming? sks.to/greenhouse
Explaining how the water vapor greenhouse effect works sks.to/vapor
The tricks employed by the flawed OISM Petition Project to cast doubt on the scientific consensus on climate change sks.to/OISM
Is extreme weather caused by global warming? sks.to/extreme
How substances in trace amounts can cause large effects sks.to/trace
How much is sea level rising? sks.to/sealevel
Is CO2 a pollutant? sks.to/pollutant
Does cold weather disprove global warming? sks.to/cold
Do volcanoes emit more CO2 than humans? sks.to/volcano
How do human CO2 emissions compare to natural CO2 emissions? sks.to/co2
Climate scientists could make more money in other careers sks.to/money
How reliable are CO2 measurements? sks.to/co2data
Do high levels of CO2 in the past contradict the warming effect of CO2? sks.to/pastco2
What is the net feedback of clouds? sks.to/cloud
Global warming vs climate change sks.to/name
Is Mars warming? sks.to/mars
How the IPCC is more likely to underestimate the climate response sks.to/underestimat
How sensitive is our climate? sks.to/sensitivity

 

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Posted by John Mason on Tuesday, 21 November, 2023


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