Long-term warming, short-term variability: Why climate change is still an issue

May 21, 2013 by Steven Phipps, The Conversation
Warming may be slower than we expected, but it’s still happening. Credit: Marc Samson

A new study published yesterday suggests that the short-term warming due to increasing greenhouse gases may be less than previously feared. However, when we look at the bigger picture, we still find that climate change is an issue that demands our attention.

The new work by Alexander Otto and colleagues, published in the journal Nature Geoscience, uses observations of surface temperature and Earth's heat budget spanning the last 40 years. This differs from many previous studies, which have been based on computer models of the climate system.

The sensitivity of our planet to a doubling of the concentration can be expressed using two different measures. One measure, the transient climate response, describes the immediate, short-term warming. This figure is the one that really matters to policy makers. The other measure, the equilibrium climate sensitivity, describes the long-term commitment once the climate system has come into balance with the enhanced level of greenhouse gases.

Using observations from the period 2000 to 2009, a decade when appeared to slow down, Otto and colleagues obtain a "best estimate" for the transient climate response: 1.3ºC. This is smaller than the value of 1.6ºC obtained when they look at observations from the 1990s instead. We might conclude from this that we need to reduce our estimates of the climate sensitivity.

However, natural variability needs to be considered as well. Internal variations within the atmosphere and oceans matter when we look at just ten years of observations. When Otto and colleagues look at the entire period from 1970 to 2009, the last decade starts to look less unusual. Their best estimate for the transient climate response is now 1.4ºC – just 0.1ºC greater than the value estimated from the last ten years.

This suggests that it might be the 1990s that was unusual, rather then the first decade of the 21st century. Indeed, another recent study by Myles Allen and colleagues evaluates a long-term climate model projection made back in 1999. That projection turned out to be extremely accurate. However, the real world warmed faster than the model prediction during the 1990s, before returning to the predicted long-term trend during the decade that followed.

So natural variability might have caused Earth to warm a little faster than expected during the 1990s. Then, during the following decade, it had the opposite effect, cancelling out some of the warming due to increasing concentrations of greenhouse gases. The period from 2000 to 2009 may therefore have seen the "pausing for breath" before the long-term warming trend continues in future.

Using observations from the past decade, Otto and colleagues derive a best estimate for the long-term climate sensitivity of 2.0ºC. This is consistent with the estimates obtained when they look at observations over longer periods of time, including the whole of the period from 1970 to 2009. The apparent slow-down in global warming over the past decade has therefore done nothing to change our best estimates of the long-term response.

This new work by Otto and colleagues refines our estimates of the , but the overall picture remains unchanged. Even medium-range climate scenarios suggest that the atmospheric will have doubled, relative to pre-industrial levels, well before the end of the current century. If our emissions of continue unabated, we still face an uncomfortable future.

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User comments : 12

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mememine69
1.3 / 5 (17) May 21, 2013
Mother Nature to God; "I show them my tides, my volcanos and my earthquakes and even God's evolution but still the human monkeys call me sick and dying and fragile and now they want to control my climate by them sacrificing my oil and my fire!"
antigoracle
1 / 5 (11) Jun 12, 2013
The period from 2000 to 2009 may therefore have seen the climate system "pausing for breath"

Wow!! The "brilliant" explanation by climate scientists. How could anyone be skeptical?
The absence of postings from the AGW Alarmist cult is quite telling, but they lurk in the darkness doing what they are programmed to do i.e. down rate the heretics.
deepsand
4.3 / 5 (13) Jun 13, 2013
AO is like a dim witted woodpecker relentlessly pecking at a block of concrete in hopes of finding a grub.
antigoracle
1 / 5 (12) Jun 13, 2013
AO is like a dim witted woodpecker relentlessly pecking at a block of concrete in hopes of finding a grub.

and so the AGW Alarmist turd, recedes back into the depths of its cesspool of ignorance, never staying long enough for fear of seeing the light.
Maggnus
5 / 5 (8) Jun 13, 2013
I find it interesting that the Otto predictions still meet the predictions of the IPCC report of 1990, albeit at the lower side. I wonder if he also took into account ocean warming. The article seems to suggest not, but that is a lot of energy being ignored if not.

Natural variability is always going to make predictions of future climate difficult. A general warming treat is still warming, even if it is slower than predictions made from data obtained almost 30 years ago. Odd that they used the 1990 report, instead of the more up to date ones.
deepsand
4.3 / 5 (11) Jun 14, 2013
AO is like a dim witted woodpecker relentlessly pecking at a block of concrete in hopes of finding a grub.

and so the AGW Alarmist turd, recedes back into the depths of its cesspool of ignorance, never staying long enough for fear of seeing the light.

You lack the humour to be entertaining, the knowledge to be informative, and
have all the charm and attraction of a deceased rat which suffered from leprosy
and incontinence.
antigoracle
1 / 5 (11) Jun 14, 2013
AO is like a dim witted woodpecker relentlessly pecking at a block of concrete in hopes of finding a grub.

and so the AGW Alarmist turd, recedes back into the depths of its cesspool of ignorance, never staying long enough for fear of seeing the light.

You lack the humour to be entertaining, the knowledge to be informative, and
have all the charm and attraction of a deceased rat which suffered from leprosy
and incontinence.

You have the knowledge and intelligence of an AGW Alarmist Turd, that spends its entire existence in darkness at the bottom of your cesspool of ignorance, feeding on filth that you occasionally surface to regurgitate.
Howhot
5 / 5 (9) Jun 14, 2013
There are two items discussed in the article, the short term warming from the CO2 greenhouse effect, and then the long term, as CO2 levels settle into a steady state. There are a lot of feedback issues not mentioned but I'm sure the author has taken them into account as well. In a short time frame one can look at the problem as a sine wave with noise added. In the short term the spikes can be pretty erratic looking, but long term, the oscillation is very apparent by doing a fourier transform on the data and extracting the log term harmonics. This is a proven mathematical approach.

So far, all that can be see for the past two hundred years is a nice hockey stick exponential. To be honest, Earth is 3D so it varies over the world but yeah I've seen some computer models having global average temp a 10C higher than 1900. +2C seems to be the non-alarmist consensus.

Is that the "cesspool of ignorance, feeding on filth that you occasionally surface to regurgitate" you wanted?
deepsand
4.2 / 5 (10) Jun 15, 2013
AO is like a dim witted woodpecker relentlessly pecking at a block of concrete in hopes of finding a grub.

and so the AGW Alarmist turd, recedes back into the depths of its cesspool of ignorance, never staying long enough for fear of seeing the light.

You lack the humour to be entertaining, the knowledge to be informative, and
have all the charm and attraction of a deceased rat which suffered from leprosy
and incontinence.

You have the knowledge and intelligence of an AGW Alarmist ... .

Thank you for belatedly acknowledging our superiority.
antigoracle
1 / 5 (9) Jun 15, 2013
So far, all that can be see for the past two hundred years is a nice hockey stick exponential.

So far that's all you want to see. Hockey stick after hockey stick have all been confirmed fabrications of the AGW Alarmists. Take a closer look at your hockey sticks and see it for the lies they are.
antigoracle
1 / 5 (9) Jun 15, 2013

Thank you for belatedly acknowledging our superiority.

Only in the feeble mind of an AGW Alarmist turd would STUPIDITY = superiority.
Just confirms the fact.
deepsand
3.9 / 5 (8) Jun 15, 2013
AO is like an insane woodpecker looking for a grub in a block of concrete.