Temperature trends

In the most recent 5 decades, global surface T (by HADCRUT4 or any other) has increased; each higher than the previous. Here we are advised by mojo to expect this trend to reverse itself soon, with soon not defined. So, what should we be looking for, and recognize as a reversal?

A single cooler year is not a reversal, as several of those have happened during our since-1966 runup. A cooler decade surely is, by above definition, but that is such a long time to wait. So, I took recent HADCRUT4 global annual average surface T data and broke it into pieces. My goal was to find the shortest multiyear ‘bin’ comparison that has not gone negative during this time. My reasoning is that if such a bin goes negative in future, it would be an early signal of reversal. Earliest signal of a (oh no!) coming ice age.

My answer is 5 years. Shorter bins have gone negative, so are not probative. Smallest 5-yr increase was 0.004 oC (2001-2005 vs. 2006-2010), so anything less than that in a future 5-yr bin would be notable.

If you are looking for a reversal, don’t start from 2015 (too hot). Maybe not 2016 either because it has been hot so far. If 2017 subsides a bit, start then and continue through 2021. If that bin is only tiny up or negative, an initial case could be made.

This is the best I can do, based on data. Cut my previous ‘decade’ (arbitrary, convenient) metric in half. If by 2021 cooling has not come, we’ll just have to keep waiting eh?

+++

It would not be entirely wrong to view the above as a wordy dismissal of ‘ice age any day now’. But there is more that ought not to be lost. Largest observed decadal increase of 0.2 oC is not itself calamitous. There are now unusually severe floods, storms, droughts, heat waves and other problems. They need attention, which is to say money. Such problems might not increase with near-future small +T, or against hope, they might.

My opinion is that ‘our enterprise’ faces a few difficult decades and neither side of the CO2 debate has clearly got better answers.

 

UAH interpretation of lower troposphere T trends has a lower slope than surface instruments; I guess y'all know this. It also has more variability among years. I repeated my analysis for that as above. There it would require 6 years of -T to show something that has not already happened during its observed overall +T pattern.

One cannot blame down-looking satellites for this. They look at a noisy place, and have been doing so only since 1978.

Slowly increasing global T is where we are. Looking for (hoping for) that to reverse is at least a 5-year task, and not most important, it seems to me. More important is to work on environmental issues facing us right now. Identify them, monetize our available responses, and get on with it. If you conclude that the human enterprise is in a great place and needs no re-tuning, well, that's just great.

 

I hope William Redoubt will expand on this comment. Evolution has populated Earth with a very large number of species, most of them with small populations and with very limited spatial ranges. A few species have very large ranges, or long migration, or important connections with other species (having other ranges).

One species with (recently) very large range, population and dependencies is us.

Globally averaged T has varying relationships with local T everywhere. So. I wonder in what way(s) evolution could undo all that.

 

Sorry bisco, I don't get that at all. Earth surface averages 55 oF (in the whacked units you use). There are species that 'win' at 20 oF and others at 150+. I smell sarcasm, but to what end?