In Nature's open access journal Scientific Reports there's a paper just out by Chris Huntingford and Lina M. Mercado about how much more warming to expect. Scientists report that even if we
didn't add any more CO2 to the air *kept CO2 at current levels in the atmosphere (around 400 ppm), temperatures over a lot of land regions would eventually increase by more than 1.5°C. (*See comment by ATTP below.) There are two main reasons for this:
- until we reach equilibrium, with as much radiation leaving the planet as comes in from the sun, the earth will continue to warm;
- the land surface warm is a lot more quickly than the ocean surface and will continue to do so until the new equilibrium higher temperatures are reached.
To how much warming are we already committed?
|Figure 1 | Warming levels for contemporary GHG concentrations. For each GCM and climate research centre named on the vertical axis, shown in green is global mean warming for rcp85 simulations, centred on year 2015. This is an ensemble average if multiple rcp85 simulations are available for any particular model. Associated global committed warming for year 2015 GHG concentrations are brown, utilising reported model climate sensitivities in IPCC 5th report. Using these calculations, then presented in red is committed warming over land only, based on model estimates of land-sea temperature contrast. In orange are normalised land warmings, accounting for differences between each modelled and observed year 2015 global warming. The latter observed value is marked as the vertical dashed black line, and is from the NCEP climatology. Warming levels of 1.5 °C and 2.0 °C are marked as vertical red dashed lines. Source: Huntingford & Mercado 2016|
|Figure 2 | Annual mean GCM-based estimates of committed warming. Maps of calculated equilibrium warming levels for contemporary year 2015 greenhouse gas concentrations, based on knowledge of individual GCM climate sensitivity, land-ocean contrast and regional pattern-scaling. Panel (a) is multi-model mean of annual warming and panel. Source: Huntingford & Mercado 2016|
Why does this matter?
The authors explain in the paper why this matters (my emphasis and paras).
Enhanced warming over land will affect terrestrial ecosystems, crop viability, glacier melt and cause other impacts, along with human health implications of higher temperatures including within cities. Increased and related leaf-level temperatures will raise vegetation respiration rates. The amount to which this will offset vegetation fertilisation due to higher CO2 concentrations will influence the global carbon cycle, and therefore also affect “permissible” emissions to constrain warming to any prescribed limit.
Raised warming could also modulate complex circulation patterns, adjusting the local hydrological cycle with implications for rainfall patterns. Detailed analysis over the coming years of high-resolution regionally-based GCM outputs will link different proposed global temperature limits to the more local features of higher land warmings and other meteorological changes. This will aid understanding of likely adaptation needed to deal with any adverse impacts at different global warming levels....
...Demonstrated here is if heavy emissions reductions prevent either value being crossed, the robust inter-model estimates of land-sea warming contrast implies significantly higher temperatures will still be experienced over land. This must be taken in to account in any debate of 1.5 °C versus 2.0 °C as a global mean threshold aspiration.
Anthony Watts makes a token protest
Anthony Watts put up an article about this with his usual "claim" headline (archived here). That was the only bit of editorialising that he did, and all that was necessary to get the deniers denying. (He just copied and pasted the press release with no links to the press release let alone the paper, as usual.)
From the WUWT comments
July 27, 2016 at 7:50 am
…Curious,…why only over land ?? UHI ?
Adrian Roman doesn't understand what is meant by equilibrium. When the amount of radiation leaving the Earth is the same as the amount of radiation coming in from the sun, then there is equilibrium. At the moment there isn't, because more energy is being kept on earth than is coming in from the sun. That's because of greenhouse gases are increasing so quickly.
July 27, 2016 at 7:55 am
What equilibrium are they talking there? Are they highly delusional? It cannot be a thermodynamic equilibrium, for obvious reasons. It cannot be even a dynamical equilibrium, for some similar reasons but probably harder to understand by some. I would really like to see their definition of ‘equilibrium’, seems to be a highly equivocated one and possible undefined.
Marcus has another question. He thinks he sees a contradiction, but it isn't.
July 27, 2016 at 7:57 am
..1) ” At present, the climate is out of equilibrium, with the oceans drawing down very large amounts of heat from the atmosphere….”
..2) ” Second, warming rates over land are far higher than those when averaged globally which include temperatures over the oceans….”
…Isn’t this a contradiction ?
Poor Marcus is having a really hard time with this press release. He doesn't understand how something can still get hotter even while it's not getting hot as quickly.
July 27, 2016 at 8:05 amDr. Deanster thinks he is on to something but I don't have a clue what's going on in his head. Maybe he is a greenhouse gas denier.
,,My understanding is, that as “global ” land temperatures increase, the Oceans become less of a heat sink, so how could they be gaining heat as it gets hotter ? Time difference ?
July 27, 2016 at 8:05 am
Where do these guys come up with this stuff??? CO2 produces NO HEAT .. and therefore whatever eventual temperature that the atmosphere attains will be a function of incomming, stored, and outgoing energy. The only relevant storage capacity on earth resides in the ocean, and I don’t see any empiric data indicating that the ocean is going to heat the atmosphere by an additional 1.5C.
This all goes back to the flawed way in which models handle incomming energy. TSI at the top of the atmosphere is not the same as SW reaching the surface, which accounts for over 99% of ocean heating. If SW reaching the surface decreases, the temp will drop, regardless of the increase in CO2.
Mark - Helsinki wrote a lot of comments, here are just two of them.
July 27, 2016 at 8:19 am
I am sick of climate science, the data sets show (for better or worse) 1.2 so these fn geniuses say 1.5, the same morons were saying much more a mere few years ago.
Junk junk junk sick of it. This is not science. I’m done
When more rain, more rain is the projection, less rain, they project less rain, 1.2c they project 1.5c
Linear pseudo think, I am sick of it.
Mark - Helsinki
July 27, 2016 at 8:20 am
They can dress this cack up as science all they want. It rubbish
FJ Shepherd does the usual denier thing of confusing diurnal variation with an overall rise in global average temperature.
July 27, 2016 at 8:39 am
I just don’t know how my region is going to cope with another degree of Celsius warming. It really scares me. As it is, in my region, every year, from January to July, we rise from -10 degrees C to +27 degrees C. A rise of 37 degrees C every freaking year. That extra one degree C rise is going to kill us all in my region. Should I beg the UN to do something for us?
References and further reading
- Current atmospheric greenhouse gas concentrations likely commit to warmings greater than 1.5C over land - Press release from ScienceDaily.com
Dong, Buwen, Jonathan M. Gregory, Rowan T. Sutton, 2009: "Understanding Land–Sea Warming Contrast in Response to Increasing Greenhouse Gases. Part I: Transient Adjustment". J. Climate, 22, 3079–3097. doi: http://dx.doi.org/10.1175/2009JCLI2652.1 (open access)