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Earth Temperature Timeline

xkcd.com

25 pointsalbertzeyer12 comments

And yet, we'll burn all the damn fossil fuels. Because: greed.

I hope some other species gets another shot at evolving large enough brains. This one's got a large brain, but it's full of bad ideas.

In laymen’s terms, how do we know this dramatic shift in the past decade(s) is directly due to human pollution? Is there any chance it’s not manmade and if so how much?

It is a man-made shift. Here's the quick-and-dirty version of the reasoning:

The earth's energy equation has three big components: sunlight in, reflected sunlight out, and blackbody radiation out. Measurements of these three items indicate that we are not currently in equilibrium. Instead, there's an excess of 0.6 Watts/square meter. That means the planet is warming.

How do we know it's us? We've increased the CO2 content of the atmosphere. CO2's absorption/emission spectrum happens to be quite strong precisely where earth's blackbody radiation is strong; it therefore reduces the energy out by blocking the blackbody radiation. A paper about this is [0]. I eyeball Figure 6a as indicating a theoretical radiative forcing of 2 Watts/square meter, given the amount of CO2 we've put into the air.

[0] https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/wea.20...

Well, over the many-thousand-year geological record, we've seen exactly one global industrialization, and also exactly one climate shift of this nature, and against all odds they're happening at essentially the exact same time. Even if we only consider that fact, while these two dramatic and extremely rare events could be unrelated, we have awfully good reason to think they're connected.

We‘ve also seen several widespread „global cooling“ conjecture phases. https://en.m.wikipedia.org/wiki/Global_cooling

Not saying it‘s all wrong, but the risk of incomplete data and wrong conclusions is always present.

Please. From your link

> The global cooling hypothesis nonetheless gained temporary popularity due to... press reports that did not accurately reflect the full scope of the debate in the scientific literature.[1]

Wkipedia style rhetoric. The „full scope“ is also neglected these days since a small minority firmly denies the severity of the issue and the „consensous“ is just the majority vote (which is not really appropriate in science).

In other words, if the loonies are right, Wikipedia might write the exact same thing about the global warming craze one day.

According to xkcd, the world has already warmed 0.8 degrees compared to the 1961-1990 average. Something that has already happened cannot reasonably be said to be "all wrong."

That‘s undisputed. But the used reference timespan isn‘t the „norm“ and it‘s not certain that we haven‘t had similar short peaks in the past 22000 years - which is what the xkcd illustration at least strongly suggests.

That objection is addressed at the 16000 BCE mark. We have had short peaks before such as the Krakatoa eruption that reduced world average temperatures by 1.2 degrees for five years. What we're now experiencing is a continuous increase that has already raised temperatures by one degree over 100 years. I think it is very unlikely that anything similar has happened before.

... Since the last ice age glaciation

In other words, only the last 0.004% of Earth history, and using the coolest point of the past few hundred thousand years as the baseline.

The baseline is the 1961-1990 average. The coolest point is 20 000 BCE whose temperature is 4.3 degrees lower than that.

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