No, change in temperature. From now to 2050 we're looking at a 0.5 C change in average temperature. You could also say change in sea level will be relatively small as well.
Averages are funny, and that's a global average so it's more pronounced at the higher latitudes. But still it's half of what we've already done since 1900. And as a percentage change in temperature in a given region, it should be fairly small.
Just intuitively it doesn't make sense that relatively small changes suddenly produce such disparate outcomes when they haven't to date.
Looking into the numbers a bit from what was shared above, I'm not wrong. 1 billion is the upper end of an estimate, with 5 million at the lower end. That's a very wide range.
> Just intuitively it doesn't make sense that relatively small changes suddenly produce such disparate outcomes when they haven't to date.
Average temperature by itself is a very misleading measure, because it does not tell you anything about how much energy is being added to the system. Different substances need different amounts of energy added to raise their temperature by 1 degree, a concept called heat capacity. The amount of energy currently being added (and not radiated back into space) to the planet is staggering, and far in excess of the ability of the oceans to absorb it: https://www.climate.gov/news-features/blogs/enso/role-ocean-...
I do not know why popular science reporting rarely mentions this.
I'm still not understanding -- how do you calculate an 0.5 C change as a percentage?
Edit: Regarding your other point, I'm sure you agree that an 0.5 C change from -0.25 to +0.25 will have a certain obvious dramatic impact. It might seem like I picked a particularly pathological example there, but if you imagine latitude on a globe or elevation on a mountain, you'll find somewhere (like the Laptev sea) hovering at that boundary and ready to cross it.
But that's only one boundary; there are many others, where the dominant plant or insect species changes from one to another, where methane gas starts to get released faster than stored, etc. So it's rather like a staircase, and when the average shifts, there's always somewhere on the planet that goes through a confusing and dramatic transition.
Average global temperature for the 20th century was 13.9°C. So 0.5C is a relatively small change, and less than half of what's already happened - and produced precious few climate refugees I might point out. I don't like using averages like that, as you rightly point out the difference in a particular region could be quite stark.
Ok, I see. So just so we're on the same page, for reference, the average surface temperature was thought to be 7.7 C in the last ice age. Converting both to Kelvin to account for the arbitrary zero point of Celsius, the 20th century was a 2.2% temperature increase relative to the ice age. Does your math agree?
I agree that a delta of 0.5 C is less dramatic than a delta of 6.2 C, but is your intuition in accordance with all that, and do you think percentage increases are useful here for building intuition? Where would you draw the line for "small" in terms of percentage change of temperature?
I also calculate that the Earth is 30% warmer than Mars, but you might want to double check my math.
Edit -- we could also consider that temperature is in most respects an exponential measure of physical quantities (E ~ e^kT). So the ratio increase in a physical quantity of interest (E2/E1) is already given, on a log scale, by an absolute temperature difference (T2 - T1).
I still stand by my intuition that if a 1 degree rise since 1900 didn't cause mass migrations, another 0.5 degrees seems unlikely to.
I think we can agree things are going to get worse and that kind of mass migration might happen over a longer time period. Just not in the next 30 years.
How are you measuring this as a percentage change? What's the denominator?
The Earth's atmospheric CO2 is up about 30% since 1900.