Thursday, September 15, 2016

XKCD nails it on climate

Was going to blog about it, but Planet3 says it all, so go read.


CapitalistImperialistPig said...

I don't think that there is any reasonable doubt about the modern anthropogenic climate change, but I wouldn't put too much faith in the xkcd cartoon, which compares millennial scale reconstructions with modern measurements at a much finer time scale. There is a certain amount of evidence that mid Holocene climate was as warm or warmer than current temperatures. See, e.g.,

We also know that that warm climate seems to ave been driven by orbital forcings that are not as large today.

Jim Eager said...

"We also know that that warm climate seems to have been driven by orbital forcings that are not as large today."

As Randall actually implies with the two captions at 18500 and 4750:

"Earth begins to cool slowly, mainly due to regular cycles in its orbit."

No doubt he could have worded them and others much better, but this is a work of popular communication, not a climate science primer. All the minor nitpicking I've seen prompts me to recall the maxim: Don't let perfect be the enemy of good.

Unknown said...

CIP #1 — from your link it appears the mid-holocene was a northern hemisphere phenomenon and that it was warmer in the summer but cooler in the winter. It's not clear to me whether the average is warmer or cooler than today.

Bryson said...

Another version of the same complaint here:

The irritating bit is that the author refers ('skeptically') to computer models in describing the reconstructions. It seems to me there's a difference between using proxies like isotope analyses and tree rings and computer models. But the notion that there's a special 'license to be skeptical' when computer models are involved is irritating. Reliability (as in 'fit for purpose') is the issue, and we have good reason to think many kinds of computational models are reliable. I suspect over-emphasis on 'truth' is part of the problem- models aren't the truth (neither is any measurement we make) but both are often reliable.

Anonymous said...

NPR (National Public Radio) has degenerated into a Republican anti-science political shill factory. In Wisconsin we now know who to blame. In Minnesota, not so much.

CapitalistImperialistPig said...

Bob Covey - Our current warming is also more pronounced in the Northern Hemisphere but winter has warmed more than summer, so the signature is opposite to that of the mid Holocene warming. There is a certain amount of evidence for significant glacial melting in Europe during the mid Holocene and later - probably due to the warmer summers.

I mention this mainly because the more informed skeptics are full of this sort of partial information, and quick to confound our current warming with those earlier ones, even though some of them are well understood from basic principles and have different seasonal signatures.

Fernando Leanme said...

I'm skeptical about computer models. Some of them are so bad they can't even match the average temperature for NY City in 2016.

CapitalistImperialistPig said...

Fernandito - Are you sure you understand what a computer climate model is trying to do?

Hint: it's not trying to precisely match the average temperature of every point on the planet. It's trying to match average temperatures over much broader areas.

Aaron said...

Are they "that way" because they do not understand, or do they not understand because they are "that way"?

BBD said...

I'm skeptical about computer models.

So is James Hansen.

Kevin O'Neill said...

Arctic sea ice extent may have been lower during the Holocene Climate Optimum, but this is confounded by several factors. The warming during the HCO does not appear uniform across the arctic, bowhead whale fossils do not indicate a lower extent, foraminfera fossils do not indicate a lower extent, and of course there was the "Scientists say the melting Arctic has opened a Northwest Passage for Pacific species to enter the Atlantic, including a tiny plankton, unseen in the Atlantic for 800,000 years." article from 2011. If extent had been as low or lower during the HCO we would expect these species to have migrated at that time.

Beach ridges and driftwood *do* indicate there was more open water around the Greenland coast, but given the other evidence available this shouldn't be taken as evidence that the arctic ocean as a whole had more open water than today.

Prof. Sven Funder, who has done much work in the beach ridge and driftwood areas, originally thought these indicated lower extent during the HCO (He has a quote or two that are favorites among the denialistas). He later became agnostic on the subject when he saw data from other geographical areas around the arctic.

BBD said...

Why argue about the HCO? It was, and now is not.

From Marcott et al. (2013):

Our results indicate that global mean temperature for the decade 2000–2009 has not yet exceeded the warmest temperatures of the early Holocene (5000 to 10,000 yr B.P.). These temperatures are, however, warmer than 82% of the Holocene distribution as represented by the Standard 5×5 stack, or 72% after making plausible corrections for inherent smoothing of the high frequencies in the stack (Fig. 3). In contrast, the decadal mean global temperature of the early 20th century (1900–1909) was cooler than >95% of the Holocene distribution under both the Standard 5×5 and high-frequency corrected scenarios. Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century, reversing the long-term cooling trend that began ~5000 yr B.P.

Climate models project that temperatures are likely to exceed the full distribution of Holocene warmth by 2100 for all versions of the temperature stack (Fig. 3), regardless of the greenhouse gas emission scenario considered (excluding the year 2000 constant composition scenario, which has already been exceeded). By 2100, global average temperatures will probably be 5 to 12 standard deviations above the Holocene temperature mean for the A1B scenario based on our Standard 5×5 plus high-frequency addition stack (Fig. 3).

Says it all.

Fernando Leanme said...

CIP, that's why I'm skeptical. Impact modeling requires the ability to model at small scales. Let's be honest, you want to make sure a giant cyclone isn't going to strike New Mexico, and Eli needs to figure out what's going to happen to California's wine. I'm more focused on showfall over Greenland, etc.

BBD said...

CIP, that's why I'm skeptical. Impact modeling requires the ability to model at small scales

You don't need skillful regional modelling to work out that the *rapidity* of global change will have severe impacts on ecosystems and therefore on us.

However, what you say is an excellent argument for intensifying research into regional modelling.