The “carbon budget” is an estimate of how much CO2 we can still emit, but still have a good chance to keep global warming from going over the 1.5°C limit into “dangerous” territory. The budget has recently been revised (upward, thank goodness) to about 420 GtCO2 (420 billion tons of carbon dioxide).
Staying within the 1.5°C limit doesn’t make us “safe” — there are still consequences of climate change, dangerous and costly, and we’re already paying the price despite not having hit 1.5°C yet. But going above 1.5°C takes us into what is best described as: nobody wants to go there.
If all of the “budget” amount of 420 GtCO2 went into the atmosphere, it would raise CO2 concentration by 50 ppm (parts per million). But when we emit CO2, only about half of it remains in the air. The other half is absorbed, mainly by the oceans and by plant life. So, our 420 GtCO2 budget translates to an increase of about 25 ppm in atmospheric concentration.
The air right now has about 410 ppm CO2. Adding another 25 will bring that number up to 435 ppm. In my opinion, that’s the number we should be looking at. Instead of a 420 GtCO2 emissions budget, we should be talking about a 435 ppm CO2 concentration limit.
That’s the kind of limit we can actually keep track of, with precision and accuracy.
[Read more here]
This chart shows atmospheric CO2, as an annual average, measured at Mauna Loa (Hawaii) and is called the Keeling Curve.
The second chart shows the Keeling Curve with the scale adjusted to show the carbon budget limit as ppm.
The final chart shows the projected Keeling Curve if we continue with BaU (business as usual), i.e., don't cut CO2 emissions. And we cross the 1.5 degree carbon budget line in 2029, i.e., in 10 years.
It's obvious that we are not going to keep our emissions low enough to prevent 1.5 degrees C of warming. Let's look at what's happening.
First, the good news. Because wind and solar are now so much cheaper than coal, the build out of new coal plants has fallen sharply, and old ones are being shuttered and being replaced by gas/renewables. Emissions from electricity generation make up roughly 25% of total emissions. Let's say it takes 20 years for all coal powered generation to stop. That means (back of the envelope calculation) that this will reduce emissions by 1.25% per annum, ceteris paribus.
Transportation is roughly 15% (globally; it's 30% in the USA.) This will fall only slowly (if at all) in early years because EVs will make up only a small proportion of the global vehicle fleet even when they reach 100% of new sales. The average life of a car in the USA is about 12 years; globally, it's closer to 20. When EVs are cheaper than ICEVs, the chances are that vehicle replacement will speed up, because EVs are already cheaper to run than ICEVs. So let's be generous and assume an average life of twelve years. That will mean that once EVs make up 100% of sales, emissions will fall by 8% per year, or 1.2% per annum of total emissions. Put together, that means, ceteris paribus, that emissions will start to fall by 2.5% per annum. However EVs won't reach 100% of vehicle sales until 2025 or later. And that glosses over the fact that we haven't yet got electric planes or electric freighters.
There's still industry (20%): fossil fuels used for smelting ores, making steel and cement and chemicals, and so on. Could we cut emissions in industry by 3 or 5% a year? Yes, with a mixture of regulation and a carbon price. There are low carbon replacements for cement; we can reduce iron ore to get iron using hydrogen (made with renewable electricity of course); we can make synthetic natural gas and gradually replace natural gas with methane generated by the Sabatier process. So let's assume that we can cut industry's emissions by 3% per year. That adds another 0.6% a year off total emissions, making in round numbers a potential cut in emissions of 3% per year.
Agriculture (cow farts and burps; land clearing and forest burning; diesel for tractors, etc) make up 25% of global emissions. We could stop land clearing and forest burning now, if we had a firm conversation with Australia, Indonesia, Brazil, Borneo and a couple of others. And we could also plant new forests or replace destroyed forests. This would actually soak up CO2 from the atmosphere, giving us negative emissions.
Now, 3% per year cut in emissions would mean a 65% cut over the next 20 years, and 70% over the next 40---assuming it began now, which it won't. That would be quite respectable if we hadn't left things so late. Remember, it's not enough for emissions to fall for the Keeling Curve to stop rising. They have to fall to zero for the accumulated atmospheric CO2 to stop rising. Global temperatures have risen about 1 degree C from the 1880s. They are now rising by 0.2 degrees C per decade. Even if CO2 emissions peak this year (thanks in part to a recession) they won't reach zero for 40 years. So global temperatures will go on rising for at least the next 40 years, and likely by at least 0.2 degrees C per decade. That will take us up by another 0.8 degrees from here. Unless we accelerate the de-carbonisation process.
Can we do that? Of course we can, if we really wanted to. We could accelerate the retirement of coal power stations, from 20 years, to, say, 15. We could encourage the take-up of EVs and the retirement of old ICEVs with tax tweaks. A carbon tax would help shift the market away from carbon-intensive processes to carbon-free ones, for example, from making iron and steel with coal to making it with hydrogen. If the funds raised via the carbon tax were distributed as a "carbon dividend" to the people, the opposition to such a tax would be reduced.
If we stopped land clearing and burning and actually started planting forests instead, net agricultural emissions would plunge. Would the public stand for a red meat tax? No. But there is vat-produced meat just starting to be produced. As we become more and more worried abut heatwaves, droughts, floods and rising sea levels, the politics could shift very rapidly
To get to zero emissions by 2050, we need to cut emissions by 14% per year, starting this year. But even 10% per year would cut emissions by 97% by 2050, which is pretty close to zero. A 7% per annum cut would reduce emissions by 90% by 2050. Not perfect, but, hell, that's still pretty good. It could be done. But it'll take willpower, willpower to resist denialists and fossil fuel fightback and ignorance and stupidity. I suspect we won't get real action until we get panic. When people start dropping like flies from the heat in the US. When Miami is flooded every day. When the summer heat in China starts killing children. When 'once in a hundred year' floods start happening every second year. Then, we'll get global co-operation. Then, something serious will be done. And until then, progress will be slow.
We won't limit increases to 1.5 degrees C. We might just manage 2.
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