Yes, the last ice age started thawing over 20,000 years ago, but that stopped a long time ago
(Part of the How to Talk to a Global Warming Skeptic guide)
Objection: Global warming has been going on for the last 20,000 years.
Answer: It is true that 20,000 years ago the temperature was some 8 to 10° C colder than it is today. But to draw a line from that point to today and say, “look, 20K years of global warming!” is dubious and arbitrary at best.
If you have look at this graph of temperature, starting at a point when we were finishing the climb out of deep glaciation, you can clearly see that rapid warming ceased around 10,000 years ago (rapid relative to natural fluctuations, but not compared to the warming today, which is an order of magnitude faster). After a final little lift 8,000 years ago, temperature trended downward for the entire period of the Holocene. So the post-industrial revolution warming is the reversal of a many-thousand-year trend.
A closer look at today’s trend, within the context of the last 1,000 and 2,000 years, makes it even clearer that today’s trend is striking — opposite to what one would expect without anthropogenic interference.
(Courtesy of Global Warming Art. See source for details on the various reconstructions tangled above.)
If you really want to play the “global warming started X years ago” game, you should talk about how we’re reversing a 5-million-year cooling trend — or go crazy and track global temperatures right back to the origins of the planet! Not that there’d be much point …
More stories in this series:
(Part of the How to Talk to a Climate Skeptic guide) Objection: Despite what the computer models tell us, there is actually no evidence of significant global warming. Answer: Global warming is not an output of computer models; it is …
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: CO2 levels are recorded on top of Mauna Loa … a volcano! No wonder the levels are so high. (image courtesty of Global Warming Art)
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: The apparent rise of global average temperatures is actually an illusion due to the urbanization of land around weather stations, the Urban Heat Island effect.
(Part of the How to Talk to a Global Warming Skeptic guide) Objection: One hundred and some years of global surface temperatures is not long enough to draw any conclusions from or worry about anyway. Answer: The reliable instrumental record …
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