Comment by jonmc12 | Hacker News Reader

Comment by jonmc12 | Hacker News Reader

Was curious how this drought compared to direct human impact on trees, quickly mashed together some facts.

There just over 400B trees live around the world, 7.3B in California. Thats 1.8% of estimated world tree population vs holding 0.5% of people population.

301M of 4.9B (6%) trees died in Texas drought of 2011. Drought in California currently accounts for 102M (1.4%) of trees in the state dying.

Also note California has about 1 tree per person in the world. The worst famine in 150 yrs would kill 30M humans / year if it happened today. This considers the % of human deaths / year by famine of 1876-1879 as a benchmark. The article would imply 72M trees dying / year per drought in California. Not sure how comparable that is given different lifespan / reproduction rates, but kinda interesting.

Worldwide people cut down 15 billion trees each year. Maybe 7B for fuel, 6.5B for paper/etc and 1.5B for lumber. If this was distributed equally (which its probably not in reality), that would be equivalent of 274M trees cut down by humans in California / yr.

The global tree count has fallen by 46% since the beginning of human civilization.

[1] http://time.com/4019277/trees-humans-deforestation/ [2] https://www.quora.com/How-many-trees-are-cut-down-a-day-for-... [3] https://www.quora.com/How-many-trees-are-in-California [4] http://www.chron.com/news/article/2011-Texas-drought-slaught... [5] https://en.wikipedia.org/wiki/List_of_famines [6] https://ourworldindata.org/famines/

Current (highly uncertain) estimates of the number of trees globally are around 3 trillion. http://www.nature.com/nature/journal/v525/n7568/full/nature1...

The uncertainties are pretty large, but it's reasonable to assume that 400 billion is very much a lower bound.

So here I come along, as a mechanical engineer who's made a living writing software and administrating servers and networks, with a more-than-passing interest in climate science and what it might mean for mankind. In just these 2 comments, I see a perfect example of what puts me off to try to wrap my head around the "debate."

First guy says there are 400B trees, down around 50% from the beginning of time. That puts the original figure at about 800B. Second guy says there are actually 3T trees presently, which would mean an almost 400% increase over the first guy's original figure. Both cite sources, which I'm sure are well researched, exhaustively written, were presented in peer-reviewed journals, and which made their authors famous, and got lots of grant money for their respective universities.

Which am I supposed to believe? That we're killing off all the forests, or we're drowning in them? It's one figure, but it makes all the difference in the argument, and the laws which might be written AROUND that argument.

I'm not asking for clarification. I'm just pointing out that there are reasonable people who are interested in the discussion, and care about the outcome, but get put off by the inconsistencies in the facts by the published reports. (And don't get me started about reading the studies themselves. They are purposely obfuscated with domain-specific language, which would require a degree to decipher.)

You assume the estimate is based on numbers of trees instead of acres of forest. Two groups may measure the same coastline using different resolutions and end up with significantly different numbers. Likewise depending on the minimum size you get vastly different tree counts.

PS: Younger forests have more trees and significantly less wood.

He's not assuming anything. He's saying garbage in, garbage out. How can there be a reasonable discussion if we don't even know what the thing is we are trying to discuss?

Read the papers. He is arguing that they are using the same definition without doing so, thus removing his credibility.

There seems to be some interesting sourcing in OPs post. The 15bn felled trees per year actually comes from the 3tn paper (it's in the abstract). So does the 46% decline since the start of civilisation:

> Based on our projected tree densities, we estimate that over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization.

So I'm not sure why the figure of 400bn was used! The paper points out that a recent Amazon study estimated the number of trees in the rainforest to be ~390bn alone. From the paper, the number of trees in the US is probably in the low hundreds of billions.

The scientists that wrote the paper specifically said (in an interview I think) that you shouldn't interpret this as that we've magically discovered 2.6tn more trees. It's not like this changes our view on carbon sinks.

The difference is that instead of taking satellite images and approximating how many trees are in a particular area, they went out and measured typical numbers of stems within an area and (I would guess) correlated that to satellite data. Some trees are more densely packed than others and the distribution of numbers of stems varies wildly with biome. There's so much variation in what constitutes a "tree" that it makes little sense to use the numbers of trees cut down for anything climate related except snappy headlines. Clearly more trees cut down = bad, but you shouldn't relate an abstract, ideal, "tree" to e.g. one ton of carbon dioxide.

A better metric might be area of forest or the amount of biomass. That smooths out variations in species and gives a nice number.

Obviously not a Californian.

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