News Section
Stories from Climate Central's Science Journalists and Content Partners

New Climate Records Focus on Earth’s Sensitivity

By Alex Kirby, Climate News Network

LONDON – You may think the prospect of climate change is alarming, a call to action to slow down our emissions of carbon dioxide and other greenhouse gases.

You’re almost certainly right. But some scientists are now suggesting you should be much more concerned than you are, because they think we may be seriously underestimating the problem.

Evidence from studies of past climate change suggest if longer-term factors are taken into account, the Earth’s sensitivity to a doubling of CO2 could also be double than predicted.

The Geological Society of London (GSL) says the sensitivity of the Earth’s climate to CO2 could be double earlier estimates.

The Society has published an addition to a report by a GSL working party in 2010, which was entitled Climate change: Evidence from the Geological Record.

The addition says many climate models typically look at short term, rapid factors when calculating the Earth’s climate sensitivity, which is defined as the average global temperature increase brought about by a doubling of CO2 in the atmosphere.

Scientists agree that a doubling of atmospheric CO2 levels could result in temperature increases of between 1.5 and 4.5°C, caused by rapid changes such as snow and ice melt, and the behavior of clouds and water vapor.

But what the GSL now says is that geological evidence from palaeoclimatology (studies of past climate change) suggests that if longer-term factors are taken into account, such as the decay of large ice sheets, the Earth’s sensitivity to a doubling of CO2 could itself be double that predicted by most climate models.

CO2′s significance

Dr. Colin Summerhayes, who led the statement’s working group, says: “The climate sensitivity suggested by modern climate models may be fine for the short term, but does not encompass the full range of change expected in the long term…”

But he cautions that there are really two “sensitivities” involved: “Climate sensitivity is what happens in the short term in response to a doubling of CO2. But the Earth system sensitivity is what happens in the longer time frame as ice sheets slowly melt, and as sea level slowly rises.

“…The IPCC focuses on… the climate sensitivity – what will happen in the next 100 years. Earth system sensitivity tells you what happens in the next couple of hundred years after that.”

The GSL’s addition also reports new data showing that temperature and CO2 levels recorded in Antarctic ice cores increase at the same time. This, says Summerhayes, “makes the role of CO2 in changing Ice Age climate highly significant.”

Atmospheric carbon levels are currently just below 400 parts per million (ppm) – a figure last seen between 5.3 and 2.6 million years ago. Global temperatures were then 2-3°C higher than today, and sea levels were several meters higher, due to partial melting of the Antarctic ice sheet.

Bad news for polar bears and for us: geological evidence and models prove rising CO2 is melting polar ice.
Credit: Alastair Rae, Wikimedia Commons via Climate News Network

If the current rate of increase (2 ppm per year) continues, CO2 levels could reach 600 ppm by the end of this century; levels which, says Summerhayes, “have not been seen for 24 million years”.

Models match palaeoclimate

The new GSL statement outlines evidence that a relatively modest rise in atmospheric CO2 levels and temperature leads to significant sea level rise, with oceans more acidic and less oxygenated. Previous such events caused marine crises and extinctions, with the Earth system taking around 100,000 years to recover.

Dr. Summerhayes said: “We now have even more confidence from the geological record that the only plausible explanation for current warming is the unprecedented exponential rise in CO2 and other greenhouse gases.

“Recent compilations of past climate data, along with astronomical calculations, show that changes in the Earth’s orbit and axis cooled the world over the past 10,000 years. This cooling would normally be expected to continue for at least another 1,000 years.

“And yet Arctic palaeoclimate records show that the period 1950-2000 was the warmest 50 year interval for 2,000 years. We should be cool, but we’re not.”

He told Climate News Network: “The main implication from my perspective is that the geological record tells us that increasing CO2 increases temperature, melts ice, and raises sea level. This we know independently of any fancy numerical model run by climate scientists.

“However, those climate scientists’ models happen to come up with about the same answer as we get from the geological record, which suggests that the modelers are likely to be on the right track.” 

Alex Kirby, a former BBC environment correspondent, is a founding journalist of Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.


By john harkness
on December 15th, 2013

Since this article never comes right out and says it, I would just like to be clear: The new finding suggests that climate sensitivity to doubling of CO2, rather than being 3 degrees C (+/- 1.5), is in fact more like 6 degrees C??

Holy S—t!

Can we panic yet?

How much worse does the news have to get before everyone starts screaming that we need to do something about this right a-freakin’-way?

Reply to this comment

By steve (long beach, ca 90814)
on December 16th, 2013

if true, I would be stunned.  what would the effect be on all the climate models that were touted to be so accurate?  and also, does this still mean the “science is settled”?

Reply to this comment

By Eric Peterson (Front Royal, VA 22630)
on December 15th, 2013

“Scientists agree that a doubling of atmospheric CO2 levels could result in temperature increases of between 1.5 and 4.5°C, caused by rapid changes such as snow and ice melt, and the behavior of clouds and water vapor.”

The models don’t model clouds or water vapor in detail so they use parameters instead and the choice of parameter settings dictates the result.  For example climate models do not model thunderstorms even though thunderstorms as a whole worldwide have a huge effect on climate.  Instead they parameterize and predict how many thunderstorms there might be in a certain area given certain conditions, then add the effects that would have occurred had they modeled them.  But without actually modeling them, they really can’t determine the exact effect on climate.

Perhaps as a results of the inability to model weather, models have a hard time keeping up with changes in the real atmosphere: There is a lot of natural .variation that is simply not modeled and as time goes on the models are starting to demonstrate long term inaccuracy (not just weather but climate).

Reply to this comment

By FishOutofWater (Sanford, NC)
on December 15th, 2013

This study determines climate sensitivity based on paleoclimate, not global circulation models or climate models that use short term data. What it finds is that longer term processes double the climate sensitivity to CO2 compared to the models that many “climate skeptics” criticize. The skeptics are right to question the models, but the skeptics error in the wrong direction. This study indicates that the IPCC has been very optimistic.

Reply to this comment

By Lewis Cleverdon (Wales)
on December 16th, 2013

Andrew - thanks for this calm exposition of what appears to be a bombshell finding.
It raises a concern - which perhaps you can assuage - in that it is hard to see how the paleoclimate studies can provide a reliable analogue for the consequences of AGW given the extraordinary pace of change in CO2ppm over the last century. To a layman it would seem that the corresponding pace of change in nominally ‘slow’ feedbacks must reflect that extraordinary rate to some degree.

For example, the news that the Yedoma areas of Russian permafrost released CH4 as an 8.3% fraction of total carbon output in 2013, when Shaeffer et al were sure of a ceiling level of 2.7% just 2 years ago, would imply that even the ‘slow’ feedbacks may be capable of far more rapid influence than is yet widely acknowledged. Taking the CH4 GWP of 86CO2e on a 20yr horizon, a 2.7% CH4 fraction gives 1.8 times the CO2e of a 100% CO2 output, while for 8.3% CH4 the multiple is 3.5. With the 2010 NOAA/NSIDC study giving a permafrost output from the moderate A1B anthro-emissions scenario of around 1.6GtC /yr by 2080, an 8.3% CH4 fraction would give around 20.5GtCO2e, or roughly 58% of the present anthro-CO2 output.

In addition, given that the study’s 1.6GtC /yr was calculated without including the acceleration due to its emissions’ warming impact, and without including both the direct and delayed reinforcements of permafrost melt by all other non-linear feedbacks, it plainly must understate the actual output of permafrost carbon to be expected by 2080 under the A1B scenario. This implies that under that scenario we could well see a 20.5GtCO2e output some years before 2080.

There is one underlying aspect of the IPCC’s new CO2e values for methane that I’d be most grateful if you could clarify. I’ve yet to see the figure of 86CO2e on a 20yr horizon, or 34CO2e on a 100yr horizon, described as the average GWP values over those periods, but if they are actually only the values at the end of those periods they would appear to heavily understate the warming that has been imposed during the periods. Could you explain which interpretation is correct ?



Reply to this comment

Name (required):
Email (required):
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.