Thursday, July 28, 2016

Even if we stopped adding CO2 today*, we'd have to prepare for more hot!

Sou | 3:25 AM Go to the first of 12 comments. Add a comment
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:
  1. until we reach equilibrium, with as much radiation leaving the planet as comes in from the sun, the earth will continue to warm;
  2. 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?

The paper has a chart showing the results of different climate models. It's probably difficult to read if you are red-green colour blind, so here's a tip. The widest bars, third from the top, are the "Year 2015 committed land warming" and the bottom bar in each group is the "Year 2015 normalised committed land warming. The top bar in each group is the "Year 2015 global warming" and the second top bar is the "Year 2015 committed global warming":

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

There is also a map showing the warming commitment in different land regions across the world. Some parts look a bit odd to me, such as coastal Australia. But who am I to argue?Other places are as you'd expect, like the high latitudes of the northern hemisphere.

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

Marcus wonders why it's only over land. As the planet warms, the land surface warms more quickly for two reasons as far as I know. The oceans have a greater capacity for heat absorption so they retain a lot more heat in total without the temperature at the sea surface rising as much. The other thing is that with warming, more water evaporates from the oceans than from the land (where there isn't as much to evaporate) and evaporation has a cooling effect.
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 am
,,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 ?
Dr. 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.
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

Huntingford, C. and Mercado, L. M. "High chance that current atmospheric greenhouse concentrations commit to warmings greater than 1.5 °C over land." Sci. Rep. 6, 30294; doi: 10.1038/srep30294 (2016).

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)

From the HotWhopper archives


  1. There is a third reason why we would see more warming if we stopped emitting CO2: we would also stop emitting the vast majority of particulate and sulfur aerosols that are currently masking a portion of the increase in warming from increasing CO2. Furthermore, that warming bump would happen very fast and be long lived.

    1. Michael Mann certainly thinks that, he has written about it. So ironically fixing global warming might increase global warming for a while.

    2. Michael Mann certainly thinks that, he has written about it.

      So has Hansen:


    3. "Faustian bargain" indeed! I did not realize scientists could be so poetic :-)

      The bit about nitrogen fertilization and increased photosynthesis due to sunlight diffusion is interesting, I did not know that.

  2. Greg Jericho has an article in the Guardian here


    Be interesting to see if the usual trolls turn up. Bert

    1. I was going to recommend the same piece, Bert. And it's hard to disagree with -

      One of the best things about the election result has been the cabinet reshuffle, which has seen Greg Hunt no longer the minister for the environment.

      I once called him the emptiest suit in the history of Australian politics, and maybe that was wrong because given how he exited the role, perhaps a better descriptor is the biggest troll in Australian politics.
      [emph. mine]

      On leaving the job Hunt, told reporters that “I feel as if my work is done.”

      No minister for the environment could look at the data of global temperatures and think their work is done – especially if the majority of their work involved pushing the con of Direct Action onto the public.

  3. FJ Shepherd's vacuous comment on a rise of 1 degC can be turned around and applied to the Ice-Age-cometh meme: "As it is, in my region, every year, from July to January, we drop from +27 degrees C to -10 degrees C. A drop of 37 degrees C every freaking year." Why worry about a drop of 5 to 7 deg C in the global average temperature?

    1. Good point. But any good denier's eyes will have glazed over before they finished your paragraph...

  4. more energy is being kept on earth [than] is coming in from the sun

    Sou, is that stated correctly?

    1. Fixed, if I understood you properly Chris. (that to than)

  5. Maybe someone has already made this point, but there are some subtleties to this. I think the paper is considering what would happen if we fixed atmospheric CO2 concentrations, not what would happen if we stopped emitting CO2. Fixing atmospheric concentrations would require continued emisssions. If we stopped emitting altogether, then we would probably not warm much more, although there might be some adjustments due to the different warming of the two hemispheres.

    There was an earlier comment about aerosol reduction causing warming even if we stopped emitting CO2. This is probably correct in the short term, but the CO2 forcing is about the same as the total anthropogenic forcing and it likely dominates the long-term warming potential. So, I think that if we stopped emitting altogether, there might be some initial warming due to the precipitation of the aerosols, and then a cooling back to something close to what we were at the time emissions stopped, as the non-CO2 GHGs decayed.

    1. Thanks, ATTP. I should have picked that up. It means the above (HW) headline is wrong, and the first paragraph might need to be tweaked. I'll see what I can do about that.


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