25 Comments
Sep 25, 2023Liked by Zeke Hausfather

Nice job. I appreciate the reference and links to the different datasets. Maybe sometime you can give us an overview of their origin. I hope this is somewhat of an anomalous spike.

A couple graphs are labeled Heamap vs Heatmap, just FYI.

Expand full comment
author

Good catch, I’ll fix those when I have a chance.

Expand full comment

Hi. Thanks for these visualizations. To clarify up front I am a climate activist and natural resource scientist. My question is about the 3rd image 'Heatmap of daily global mean surface temperature anomalies back to 1958 relative to the 1991-2020 baseline period.' I'm wondering how you chose the baseline period in general and why you chose 1991-2020 for this visualization. This choice of baseline is the basis for everything in the image, so as feedback, I think it would be good to explain this to your readers as well:-) Thanks in advance for your reply! Appreciate your work!

Expand full comment
author

That’s just the default baseline period used by the reanalysis product. You could just as easily use 1951-1980 or any other one. Since the dataset only goes back to 1958 extending it to use a preindustrial baseline would require normalizing it to another dataset that goes that far back.

Expand full comment

I disagree that you can just pick any baseline. That data tells a story in relation to that baseline, so it DOES matter what period you pick for the baseline. Pick a cooler baseline period and the current year's data looks hotter, pick a hotter baseline and the current data doesn't look as hot. So why is 1991-2020 the baseline of the reanalysis product (and what is that?)? These are important data validity questions you should be able to answer. Not that it's "just the default baseline.." WHY is it the default? There should be scientificly valid reasons for this or the stories you are telling with the data can be questioned.

Expand full comment
author
Sep 26, 2023·edited Sep 26, 2023Author

In all of the anomaly plots as well as in most of climate change, what you care about are relative differences — e.g., year X is hotter than year Y. In that case, the baseline is largely unimportant. There are no data validity issues here. If you think the story is affected by the baseline, then you'll have to tell me what story you're trying to tell.

Expand full comment

I second Andrew's point that the relative differences are what matter. That said, even if you're trying to tell a story by making the colours as red as possible, you quickly run out of deeper red colours if you move the baseline further into the past, which can only be solved by dimming the reds (since displaying infrared is impossible) so it seems like the change is more gradual, but then your relation between colour temperature and actual temperature difference becomes non-linear (it will become somewhat log-scale-like), which is deceptive.

Expand full comment

I'm interested in the potential that the next several years might be cooler ("regression to the mean"), just as the years after 1998 were quite a bit cooler than in 1998. Some of the graphic images tend to illustrate this with regard to the post 1998 period, based on color coding. This gets at whether 2023 is "typically anomalous" as in the 1998-2008 period, or whether something more serious is happening. It would be nice to see a more mathematical analysis that sets up statistical, hypothesis testing. Thoughts?

Expand full comment
author

If anything we’d expect 2024 to be warmer given that we are still early in the El Niño cycle. But I wouldn’t be surprised if it takes until 2030 to pass 2024 temperatures (e.g. as we saw after 1998 or 2016).

Expand full comment

These visualizations really hammer the point home. You could really feel the difference here in New York this summer. Definitely concerning that 2024 could be even worse given El Niño…

Expand full comment

"Somewhat surprisingly, the increase in global temperatures DUE TO? human-driven warming is clearly..."

Expand full comment

I really appreciate these posts. I learn so much each time. Thank you. However, full disclosure ... I am not a climate scientist, so my question may be stupid.

I am interested in the last graph that represents 'Global monthly mean surface temperatures'. How is it that the period between October and April is so much lower that the middle if the year, when the southern hemisphere is deep in our summer season and temperatures down here soar? Is it just there is less landmass?? Is it that the north hemisphere cold shifts the dial towards a cool global mean?

I ask because in Australia we're are facing at least a few summers that will eclipse the European heat registered this year, yet this appears lost in the graph.

Expand full comment
author
Sep 26, 2023·edited Sep 27, 2023Author

Yes, you got it. The southern hemisphere is mainly water, so it's temperature varies less than the northern hemisphere, which has a lot more land. Interestingly, the Sun is actually closest to the Earth in Jan., which reduces the N-S difference. In 10,000 years, when the Sun is closest in NH summer, there will be an even bigger annual cycle.

Expand full comment

Thank you, Andrew. That is now crystal clear.

Are there any similar graphs floating around that look at mean surface temperature over land mass? I appreciate that ocean temp is a huge part of the big cycle, but if someone is trying to explain how soaring temperatures will affect human communities the 'global mean' graph paints a different picture. It looks like the greatest heat impact is being felt in the global north, which is a long way from the lived reality in the global south.

Expand full comment

While 90% or so of the excess heat being trapped by our greenhouse effect on steroids has gone into the oceans, ocean temperature doesn't respond like air temperature. This is because of the much greater heat capacity of sea water.

For example: At 20 C, a cubic meter of water has 1.22e9 (1.2 billion) Joules of energy

A cubic meter of air has 246,120 Joules

So, Water holds 4,875.6 times as much heat as air at that temperature, by my calculation.

" "One way to summarize this is to say that the higher the heat capacity, the greater the thermal inertia, which means that it is harder to get the temperature to change. This concept is an important one since Earth is composed of materials with very different heat capacities — water, air, and rock; they respond to heating and cooling quite differently."

https://www.e-education.psu.edu/earth103/node/1005

Expand full comment

Thank you, Richard. That is hugely helpful.

It also draws into clear focus the difference of what scientists mean when they refer to temperature vrs what the media interprets in relation to soaring temperatures around human communities.

Is there any modelling that specifically looks at the temperatures being and to be experienced by human communities in the north and south?

Expand full comment

I wonder if 2024 temperature anomalies will be even higher than 2023... Looks September will be close to the record from February 2016! Highest monthly anomaly in ERA5. Hard to imagine hotter than this, but that might be where we're heading❗

Expand full comment

Hi Zeke and others. I’m new here. Does anyone understand the substantial discontinuity between the last few months(?) data and the Before Times? What are the possible causes?

I’m not an engineer, but it seems to me this system is running substantially outside normal parameters right now. Either it’s received a brief hard push and will gradually return to quasi-normal, or something new is in play and we don’t know what’s next.

Expand full comment
Oct 1, 2023·edited Oct 1, 2023

El Nino and the undersea eruption near Tonga are adding to the heat from AGW. That eruption put a huge amount of water vapor into the upper troposphere, a greenhouse gas.

But El Nino also added to the global temperature of record warm years 1998 and 2016.

El Nino, La Nina and neutral years are all warming however.

Expand full comment

no discussion of climate chgne and co2 is complete without recognising the biggest emitters- the political/industrial elite 1% flying around pretending to save it by being responsible for 25% and the Pentagon - maybe the US could try negotiation instead of provoking proxy wars.

Expand full comment

ZH, thanks again for preparing an informative presentation. What I am going to say is independent of your analyses: My hope is that eventually the "climate research community" will agree upon one reanalysis model, globally and for each hemisphere.. Again, thanks. zf

Expand full comment
author

Unlikely. There's a benefit to having several reanalyses: e.g., you can compare them to see if they agree, and the degree of agreement gives you a sense of the uncertainty. And I don't see many disadvantages (if any) to having a few reanalyses. On this topic, they are all in agreement.

Expand full comment

Point taken. I do understand. As measure of "uncertainty" it a very good argument. Overtime, there could be a convergence of sorts amongst the reanalysis models. Other than a visual, what metric would be good for making that conclusion? Some kind of SE over models, i.e. precision increasing as SE decreased? Thank you.

Expand full comment
author

What people frequently do is just put lines for all of the reanalysis on a plot. Alternatively, you could calculate a correlation coefficient between the lines, or some kind of root mean square difference. There are lots of ways to handle it that will be determined primarily by what problem you’re trying to solve.

Expand full comment