The climate bathtub

It seems more and more clear that emissions have peaked.  

China, responsible for 25% of global emissions, installed as much solar last year as the rest of the world combined.  It looks as if it's going to do the same this year.  In addition, EVs now make up 48% of China's new car sales, and at the current growth rate, this will reach 60% within a year and 70% within 2 years.  This has led several respected analysts to conclude that Chinese emissions have passed a secular peak, or will do so this year, after a big jump in emissions as growth resumed after Covid lockdowns.  Emissions for Europe and the USA have been falling for a couple of decades now, and the reason global emissions continued to rise was emissions from China.  If Chinese emissions have peaked, even if the year-to-year decline is small, global emissions have prolly peaked too.

The second reason is more general.  Battery prices have halved this year.  Last year, Lazard estimated that adding 4 hours of storage to solar would add $14/MWh to the cost.  With battery prices halving, this means that we add 8 hours of storage to the cost of solar for the same cost (more or less) as we added 4 hours previously.  This will mean that between latitudes 35 or 40 north and south, we can run the grid on solar, more cheaply than on coal.  The plunge in battery costs also means that EVs are now cheaper than petrol cars, not just to buy but to run.  For example, in Australia, BYD plans to introduce an EV which will sell for less than A$30K, about the same as the cheapest Toyota petrol Corolla.  EV sales will, as in China, completely replace petrol (gasoline) sales.

Over the next 15 to 20 years, electricity generation and land transport will mostly transition to carbon-free.   As coal power stations in developed countries age, they'll be shuttered, not just because of environment reasons but because they will be too costly. "Wait a minute," I hear you cry, "what about the extra electricity demand from EVs?"   Because solar plus storage will be cheaper than coal and baseload gas, this extra demand won't be met by building new coal power stations, but by new solar, rooftop and utility scale.  

Since generation and land transport make up roughly 50% of global emissions, that means emissions will halve over the next 2 decades.   If you add in replacing oil and gas heating for homes and offices with electric heat pumps, and efforts to switch to carbon-free steel, the decline over the next 15 to 20 years could be 60 or 70%.

That's good, right?  It means temperatures have peaked and will start falling this year?  Not quite, no.

Imagine the atmosphere as a giant bath.  The level of water in the bath represents the level of CO2 in the atmosphere.  The taps are on full, day and night, filling the bath.  There is a tiny trickle out of the bath, caused by natural weathering (CO2 dissolves in water, and reacts with rock to produce carbonates, which removes that CO2 from the atmosphere).  Even if we turned off the taps completely, the bath would take a 1,000 years or more to empty.  

Global temperatures are proportional to the level of CO2 in the atmosphere.  Or, taking the differential, the rise in temperatures is proportional to the level of emissions.  In other words, using our bath analogy, to the flow of water out of the taps.  So even though the flow of water out of the taps is going to fall from now on (the levl of emissions has peaked), the level of water in the bath will continue to rise, just more slowly (temperatures will keep on rising).   If we halve emissions, we will halve the decadal increase in temperatures.  But they will still be rising (just more slowly).  To stop temperatures rising altogether, we need to stop the level of bathwater rising.  In other words, we need to cut emissions to below the trickle escaping past the bath plug, the trickle caused by natural processes.  

What about "negative emissions" or "carbon offsets"?   These are the equivalent, in our analogy, of taking a scoop of water from the bath, and pouring it into a hole in the ground.  Except, it's not a scoop, but a tiny doll's house teaspoon.  And obviously, if the taps are on full, it's completely pointless.  Once the taps are turned off, then, yes, it starts making sense.  But we'll still need something bigger than a miniature teaspoon to do anything worthwhile.

Yes, it is good news.  The taps are being turned down, and one day, in perhaps 30 or 40 years, will be finally turned off altogether.  But temperatures will go on rising, but the good news is that they will be rising more slowly.  If we do in fact halve emissions over the next 15 to 20 years, we will also halve the decadal rise in temperatures.  And if we halve them again over the next 15 years, we will halve the decade-by decade rise again, and so will avoid a 2 degree rise since pre-industrialisation, taken (for practical reasons) to be the average temperatures from 1850 to 1900.  

A 2 degree rise is bad news.  But it is better than 2.5 or 3 degrees.  Much, much better.  Cautious optimism is in order.