Climate change from a deep time viewpoint

Recently the government released a national climate assessment and not long before that the IPCC released their most recent major report. So it is time for all those who want to continue doing what they are doing to deny that any of this is correct. So rather than hammer on the same old talking points (which makes GG even grumpier), let’s look at this slightly differently.

It is easy to show that carbon dioxide has been increasing in the atmosphere for more than 50 years, and it is also pretty easy to show that this is from burning fossil fuels. This isn’t usually in dispute, but if you want, check into the changes in the isotopic composition of atmospheric carbon dioxide: it is rapidly growing richer in light carbon, which is a signal of fossil fuels.

Anyways, it is typically at this point where disagreements emerge. The climate community is very proud of their models and points to them as showing what will happen if CO2 levels continue to increase. Now these models represent a huge amount of work, but GG feels sometimes they don’t understand why models aren’t too convincing outside their community. Perhaps they don’t notice the occasional epic fail in a weather forecast, the inability to forecast a La Niña or El Niño event reliably or the continued uncertainty around some even longer term oscillations in the atmosphere that defy these models. And GG recalls that less than 15 years ago these models were predicting increased ice cover in Greenland (that prediction certainly went south). And there has been a long-standing problem with explaining the earth’s climate back in the times when there were no glaciers (in the Cretaceous, say, or Eocene) that suggest there could be stuff missing in climate models [and yes, GG is aware of some recent papers that maybe have solved this and maybe we’ll discuss later, but this still needs to be sorted out]. So GG understands a distrust of model predictions. But you know what? Models can be wrong in both directions: they might be underpredicting problems, too.

Now the basic objection raised is that the models are missing a large negative feedback, which means that as carbon dioxide increases, something else changes too that makes things cooler. The most popular suggestion is that water vapor will rescue us by generating more clouds or fewer clouds (depending on the place) and balance things out. This line of argument rapidly descends into arguments over coefficients in the models that seem so esoteric that lots of folks think this is like angels dancing on the heads of pins and so they tune out. Ugh.

Being of a geological mindset, GG suggests looking at the Earth’s history instead. We have lots of ways of estimating temperature in the past and quite a few for getting a handle on carbon dioxide in the atmosphere. Looking in ice cores we see the warm interglacials were accompanied by higher levels of carbon dioxide and major glaciations low levels. As more astute readers might know, there is an interesting timing issue in the details that is caused by the initial forcing of that climate change being changes in the earth’s orbit, but let’s not sweat that and instead look even farther back. We can look at the end of the Paleocene and find a rather rapid increase in carbon dioxide in the atmosphere and ocean. At the same time we see a massive increase in temperatures (something like 5 degrees C or 9 degrees F in ocean temperatures). Seems like the magic negative feedback failed to rescue the planet back then.

Don’t like those proxies? How about something simpler: the presence of continental glaciers. These leave really easily identified remains in the rock record. We look back before 35 million years ago and we have to go all the way back to the late Paleozoic, some 280 million years ago, to find big glaciers—and they were really big. What was carbon dioxide back then? Really low any way you slice it, but in some ways the simplest thing to look at is what is in the rocks early in the glacial period and just before. What you find are massive coal deposits. In fact, most of the coal we’ve burned and then lots more comes from this time period. The burial of all this coal—the largest coal deposits in Earth’s history—represents a massive reduction in carbon dioxide in the atmosphere. And yet  those negative feedbacks from increasing CO2  just don’t seem to show up. Pretty much in every way you look at it, increasing carbon dioxide makes the world warmer.

Now to be fair, there is a major negative feedback out there. Increasing carbon dioxide will lead to increased chemical weathering of rock. This takes carbon dioxide and combines it with calcium or magnesium in rocks to create limestones and dolomites in the oceans. The only problem is that this is a very slow process taking tens of thousands of years to recover carbon dioxide from the atmosphere. GG can’t speak for you, but he doesn’t think it wise to wait for this process to clean up our mess.

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