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In April 19, 2019, there was a public debating event called "Happiness: Capitalism vs. Marxism" featuring Canadian psychologist Jordan B. Peterson and psychoanalytical philosopher Slavoj Žižek as the two speakers. During this so-called "debate of the century", Peterson (1:55:32 in the video of the event) reiterates an argument made earlier by Žižek that there were more forests now in the Northern Hemisphere than 100 years ago.

Is this claim correct?

Schmuddi
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SSimon
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    @Maxim That only goes back a few decades. In any case the last hundred years are not the most important. There was huge deforestation in North America between 200 and 100 years ago. – DJClayworth Apr 20 '19 at 15:26
  • Related question: [Is only 4% of original forest left in the US?](https://skeptics.stackexchange.com/questions/43182/is-only-4-of-original-forest-left-in-the-us/) – Oddthinking Apr 20 '19 at 18:43

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There are several news reports 1, 2, 3, which are all mentioning this study, that is unfortunately not open-source. The findings were

The research suggests an area covering 2.24 million square kilometers - roughly the combined land surface of Texas and Alaska, two sizeable US states - has been added to global tree cover since 1982.

But it is also mentioned, while the northern hemisphere has more trees, south America has lost a lot and the diversity of the trees went down.

South America Tree loss Image Reference

I know this is not a hundred years ago, but only 35 years. Given the fact that he held a speech and the claim sounds very similar (only time is offset, but on the same scale) and he retweeted a similar news story, were the claim was

“Deforestation has stopped in wealthy countries. Europe’s forest area grew by more than 0.3% annually from 1990 to 2015. In the United States it is growing by 0.1% annually.”

I am pretty certain he didn't mean exactly a hundred years ago.

Maxim
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  • Wow. Thank you. Is it true that most people live in Northern hemisphere? – SSimon Apr 20 '19 at 15:59
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    Unfortunately, the time span that is covered by the article you refer to is too short to address the claim asked in the question. The 1980s were a time in which the impact and the dangers of deforestation became very visible. It's not surprising that we see an absolute increase since then. But what about the preceding 65 years, a period in which environmentalism was not exactly well-developed? What if the absolute loss of forested areas during that time in the Northern Hemisphere was much larger than the gain since 1982? – Schmuddi Apr 20 '19 at 16:08
  • @SSimon [Yes](https://www.google.com/maps/@-2.4608605,-54.3483798,4z). But that isn't really relevant since this is a global issue: oxygen is a gas and difuses freely across the entire planet, so you can't make a useful breakdown by hemisphere. – terdon Apr 20 '19 at 16:40
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    I don't understand the labeling in that figure. Is the net gain for e.g. Europe larger than the gross gain? – Anyon Apr 20 '19 at 20:40
  • @Anyon It is written net **change** not net gain. That means the positive and the negative **gain** (total change). The net **gain** is the positive surplus – Maxim Apr 21 '19 at 08:03
  • Along the lines of the previous comment: how can the net change be larger than the gross gain? Somehow it seems the darker green and lighter green should be interchanged in the legend. – ZeroTheHero Apr 21 '19 at 20:11
  • @ZeroTheHero I suspect the same, not least because the data for South America looks rather weird. Why would the apparently negative gain be counted separately from the loss? And if there is both loss and **negative** gain, how can the change be positive? – Anyon Apr 22 '19 at 00:13
  • @Maxim Sure, it's written net change. I made the (natural?) interpretation that a positive net change corresponds to a net gain. The point still stands though, if there is a gain g>0 and a loss l>0, then I would expect the net change to be g-l – Anyon Apr 22 '19 at 00:26
  • @Anyon the legend labels for "gross gain" and "net change" should be switched, then it all makes sense. – 410 gone Apr 25 '19 at 09:06
  • This doesn't answer the question, which was about 100 years. 37 years is not 100 years. It's not remotely 100 years. – 410 gone Apr 25 '19 at 09:09