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In Bill Gates' 2010 TED talk, Bill Gates: Innovating to zero! [YouTube], Gates mentions that he has

asked the top scientists on this several times: Do we really have to get down to near zero? Can't we just cut it in half or a quarter? And the answer is, until we get near to zero, the temperature will continue to rise. And so that's a big challenge. It's very different than saying, "We're a twelve-foot-high truck trying to get under a ten-foot bridge, and we can just sort of squeeze under." This is something that has to get to zero.

[emphasis mine]

This is in relation to the emissions that we are producing and the need for these levels to go right down to near zero. This intrigues me as it's a very substantial claim.

Do the Climate Emissions need to go right down to near zero to stop the temperatures rising?

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    He almost certainly means net emission.
    – DJClayworth
    Commented Jan 24, 2020 at 16:06
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    @DJClayworth if you look at the full transcript he says: "Now, we put out a lot of carbon dioxide every year — over 26 billion tons... somehow, we have to make changes that will bring that down to zero". So he means the gross anthropological amount, not the net amount. singjupost.com/innovating-to-zero-bill-gates-full-transcript
    – DavePhD
    Commented Jan 24, 2020 at 16:14
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    @DavePhD he means zero - and as it happens, net zero effectively requires anthropogenic additions to the carbon cycle to go to gross zero anyway, because of the limited scope for increasing sinks.
    – 410 gone
    Commented Jan 24, 2020 at 20:02
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    @Möoz You'll be far better off asking this on Earth Science - that's where the genuine experts are. Here, you've just received a pseudo-scientific answer.
    – 410 gone
    Commented Jan 24, 2020 at 20:04

1 Answer 1

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Below is Fig. 3 of Global Carbon Budget 2018 Earth Syst. Sci. Data, vol. 10, pages 2141–2194, 2018.

enter image description here

Here, it is shown that current annual emissions are about 11 Gigatons of carbon (GtC), of which the land and ocean are incorporating about 5 GtC.

So at a minimum, a reduction by a factor of 5/11 is needed to stabilize the concentration of carbon dioxide in the atmosphere. However, this would only be a temporary stabilization because the ocean would eventually approach saturation with carbon dioxide. Similarly, as explained in CO2 is making Earth greener—for now, land plants are currently taking up a high net amount of CO2, but if the CO2 concentration started to stabilize, this amount would decreased to the historical lower amount similar to the early portion of the above graph, where only about 1 GtC is being incorporated annually into the land and ocean.

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    You've completely misunderstood the carbon cycle. This answer is simply wrong. The detail is in the IPCC documents - go read up on the outputs from AR5 WG1. ipcc.ch/report/ar5/wg1 Please don't just guess at an answer based on a naive reading of a graph.
    – 410 gone
    Commented Jan 24, 2020 at 20:00
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    @EnergyNumbers perhaps you can write a better answer? As someone who knows almost nothing about environmental science, the "naive reading" of the graph seems correct to me. If it's wrong, we should fix that.
    – PC Luddite
    Commented Jan 25, 2020 at 4:05
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    As a simple analogy, let's say I always spill a little bit of water when I pour it from my bottle into a glass. Let's say I'm typically spilling 50ml of the 500ml that come out the bottle. There is no reason to assume that my spillage would go down to zero if I only poured 450ml to begin with
    – themirrorconspiracy
    Commented Jan 31, 2020 at 0:48
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    @themirrorconspiracy after decreasing emissions, at first the ocean and land would take up about the same amount as currently, but then as the concentration of CO2 in the atmosphere declines and the upper layer of the oceans becomes more-saturated, the amount taken up would decline. That's what the answer is trying to communicate.
    – DavePhD
    Commented Feb 16, 2020 at 17:00
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    If it is currently in equilibrium (citation-needed) and the concentration in the atmosphere declined, wouldn't the ocean expel CO2 into the atmosphere? (I am no expert here, and expect to be contradicted. I am just explaining why I am unconvinced.)
    – Oddthinking ♦
    Commented Feb 24, 2020 at 23:12

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