A study has been done that showed the slowing of average forward speeds from 1949 to 2016:
https://www.nature.com/articles/s41586-018-0158-3
"The magnitude of the slowdown varies substantially by region and by latitude, but is generally consistent with expected changes in atmospheric circulation forced by anthropogenic emissions. Of particular importance is the slowdown of 30 per cent and 20 per cent over land areas affected by western North Pacific and North Atlantic tropical cyclones, respectively, and the slowdown of 19 per cent over land areas in the Australian region."
So, that combined with heavier rain rates caused by warmer air holding more moisture would mean GW does, indeed, mean more and more extreme heavy rain events from landfalling TCs.
I learned something new. All I had heard from Joe Bastardi and others about Harvey was that GW had nothing to do with it...just that it happened to move very slowly. Well, if GW causes slower moving TCs on average, then GW INDIRECTLY causes an increase in the number of and severity of cat. rain events from TCs.
Not that this can't be significant, but 67 years is not enough data to make any conclusions, IMHO. I've built too many models of other coupled, chaotic, non-linear systems to have any faith in this. At the very least, I wish they had gone back into the 30s in the study.
I've watched this for years now.
I've especially watched the north pacific. I have never seen it such as it has been now for awhile. I've watched "the blob" mature and dissipate - and no one still, to my knowledge, knows what caused it. While the US has experienced a massive moisture flow this summer, I experienced a severe (on-going) drought in Terrace, BC - rain forest country. An extremely interesting question, to me, is - what signal went out over the pacific to tell the steelhead that, this summer, they should enter the river three weeks earlier than they have ever done so ( in recent decades, at least)? It most likely is that chaotic pattern over the north pacific and the expectation of very low river levels - that make the journey much more difficult to their home waters.
It's a complex system, and not easily modeled. The use of limited data adds to that problem.
Thanks Larry,
This is a good point. Do you have a link to the actual paper I can look at?
The abstract has wording that shows bias. "These changes vary by region and time of year, but there is evidence that anthropogenic warming causes a general weakening of summertime tropical circulation"
An objective scientist, looking only for empirical data to form their opinion, should not start with a statement that shows their opinion about warming. However, the funding of many studies is dependent on the wording of and assumptions.
I don't know if that's the case here but funding to study problems caused by humans is much more available to study funding of natural causes and especially to study a problem vs to it not being a problem. So the scientists asking for funding make it a problem and one caused by humans as part of their initial assumption, then look for the evidence.
Despite my comment above, there is no question that the atmosphere can now hold 5% more moisture than it did 150 years ago and rains have increased in most areas.
World drought has decreased and crops are benefiting by 25% because of climate change and the increase in CO2 but flooding has also increased..........no question about it. The factor that you mention here could also be contributing to high end excessive rain events, including tropical cyclones.
When you decrease the meridional temperature gradient by warming the highest latitudes the most, the atmosphere does not need to work as hard to try to balance the heat differential with latitude.
This reduces some types of extreme weather, like violent tornadoes but increases others, like excessive rains.
Hey Mike,
The full study is paywalled. I too haven't seen it.
I see your point about them emphasizing AGW. But we know the globe has warmed, regardless of whether or not the bulk of it has been due to AGW. Do you think it makes sense that a warming globe, regardless of the main cause, would tend to lead to slower moving tropical cyclones, especially well away from the tropics?
Hi Larry,
While you were typing the last comment, I was adding to my first one. Yes, it does make sense that some weather systems will slow down.
One way to imagine it would be if we made the entire planet the same temperature.
There would not be much of a jet stream or atmospheric energy derived from a temperature contrast or the need to move warm air from the south to the north and vice versa...............so weather systems would not move very fast.
At the same time, less need to balance the heat differential from south to north plays a role too in the strength of many systems because they have less potential energy.
Hurricanes are supposed to get stronger because of warmer ocean temperatures. This seems like sound meteorology to me. However, hurricances also take excessive heat in the tropics(relative to the higher latitudes) out of the atmosphere.
It's not the absolute temperature but the relative temperature(differential from north to south) that is a factor here. Highest latitudes warming the most has decreased this.
Thanks cfdr and Mike for your replies.