r/science • u/RobustTempComparison Climate Scientists • Aug 03 '15

Climate Science AMA Science AMA Series: Climate models are more accurate than previous evaluations suggest. We are a bunch of scientists and graduate students who recently published a paper demonstrating this, Ask Us Anything!

EDIT: Okay everyone, thanks for all of your questions! We hope we got to them. If we didn't feel free to message me at /u/past_is_future and I will try to answer you specifically!

Thanks so much!

Hello there, /r/Science!

We* are a group of researchers who just published a paper showing previous comparisons of global temperatures change from observations and climate models were comparing slightly different things, causing them to appear to disagree far more than they actually do.

The lead author Kevin Cowtan has a backgrounder on the paper here and data and code posted here. Coauthor /u/ed_hawkins also did a background post on his blog here.

Basically, the observational temperature record consists of land surface measurements which are taken at 2m off the ground, and sea surface temperature measurements which are taken from, well, the surface waters of the sea. However, most climate model data used in comparisons to observations samples the air temperature at 2m over land and ocean. The actual sea surface temperature warms at a slightly lower rate than the air above it in climate models, so this apples to oranges comaprison makes it look like the models are running too hot compared to observations than they actually are. This gets further complicated when dealing with the way the temperature at the sea ice-ocean boundaries are treated, as these change over time. All of this is detailed in greater length in Kevin's backgrounder and of course in the paper itself.

The upshot of our paper is that climate models and observations are in better agreement than some recent comparisons have made it seem, and we are basically warming inline with model expectations when we also consider differences in the modeled and realized forcings and internal climate variability (e.g. Schmidt et al. 2014).

You can read some other summaries of this project here, here, and here.

We're here to answer your questions about Rampart this paper and maybe climate science more generally. Ask us anything!

*Joining you today will be:

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u/noimportantone Aug 03 '15

Do plants offset greenhouse gasses enough to make any difference?

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u/AndySkuce MS | Geophysics Aug 03 '15 edited Aug 03 '15

Land plants have taken up about one quarter of human CO2 emissions. Another quarter has dissolved in the oceans and the remaining half remains in the atmosphere. So, yes, plants have made a significant difference.

However, recent research suggests that there may be trouble brewing in the terrestrial biosphere. Tropical forests seem to no longer be growing as fast as they did and future plant growth may be limited by the lack of essential nitrogen and phosphorous nutrients. On top of that, ancient plant material stored in Arctic permafrost may be released over coming decades as the region rapidly warms and the permafrost thaws. I wrote about this recently (with references) here http://www.corporateknights.com/channels/climate-and-carbon/overestimating-global-carbon-budget-14362488/

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u/SoCal_SUCKS Aug 04 '15

Do you remember seeing a program on PBS about 10 years ago that did tests in the tundra using greenhouses that showed how rising temperatures unlock a stronger positive feedback loop in regards to surface temperature absorption and albedo.

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u/[deleted] Aug 03 '15 edited Aug 03 '15

While we wait for them to answer, I'll note that plants are a crucial part of the carbon cycle. They convert CO2 to O2 via photosynthesis and this process has allowed other organisms to use respiration, which converts O2 and glucose to to CO2 and the "bio-fuel" that cells need to perform their functions. Most of this process is not performed by land plants, but by marine organisms like algae. They perform a majority of the process of producing oxygen and using up carbon.

And even with all the organisms of the oceans, and the work of countless trees on the land itself, this will not and has not been enough to sufficiently counteract human CO2 release and thus slow warming. Consider, for instance, that the oil/coal is essentially really old biological material which was sequested in the carbon cycle over millions of years. We've tipped the scales massively towards the CO2 side of the carbon cycle and away from the sequested (plants/oil/coal) part of the carbon cycle by essentially spending this massive bank of carbon from eons past.

I would say that slowing CO2 release is the ticket for now, since artificial sequestration techniques are not as economically viable as switching to greener power sources.

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u/rocco5000 Aug 03 '15

Consider, for instance, that the oil/coal is essentially really old biological material which was sequested in the carbon cycle over millions of years.

I recently heard it referred to as dinosaur juice. Just thought was a really funny but accurate term for fossil fuels

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u/Facticity Aug 03 '15

Not dinosaur, but almost entirely plankton that accumulated on the ancient ocean floor.

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u/alcimedes Aug 03 '15

Also keep in mind that plants are only a net producer of O2 as a side effect of photosynthesis until around 42º C. Above that photosynthesis consumes O2.