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Rise In Atlantic SSTs Linked To Reduced Air Pollution

October 1, 2017
tags: ,

By Paul Homewood

I mentioned this piece of research a week or so ago. Although it is from 2013, it is still highly relevant.



New research from the Met Office has raised the possibility that man-made aerosols, industrial pollution, may have had an impact on the number of Atlantic hurricanes.

The paper, published in Nature Geoscience, suggests aerosols may have suppressed the number of Atlantic hurricanes over the 20th Century and even controlled the decade-to-decade changes in the number of hurricanes.

Researchers found that aerosols make clouds brighter, causing them to reflect more energy from the sun back into space. This has an impact on ocean temperatures and tropical circulation patterns, effectively making conditions less favourable for hurricanes.

This interaction between aerosols and clouds is a process that is now being included in some of the latest generation climate models.

Dr Nick Dunstone, a Met Office climate prediction scientist and lead author of the research, said: "Industrial emissions from America and Europe over the 20th Century have cooled the North Atlantic relative to other regions of the ocean. Our research suggests that this alters tropical atmosphere circulation – making it less likely that hurricanes will form.

"Since the introduction of the clean air-acts in the 1980s, concentrations of aerosols over the North Atlantic have reduced and model results suggest that this will have contributed to recent increases in hurricane numbers. On the other hand, the reduction in aerosols has been beneficial for human health and has been linked to the recovery of Sahel rains since the devastating drought in the 1980s."

It has long been known that North Atlantic hurricane activity has distinct long-timescale variability. Dr Doug Smith, a Met Office research fellow and co-author of the study, said: "We saw relatively quiet periods between 1900-20 and then again from 1970-80, and active periods between 1930-60 and since 1995. On average, active periods have 40% more hurricanes."

When the authors include changes in man-made aerosol emissions in the latest Met Office Hadley Centre model, which includes a comprehensive treatment of aerosol-cloud interactions, they can reproduce much of the decade-to-decade variability in Atlantic hurricane activity. This supports evidence of a link between the two.

Dr Ben Booth, a Met Office climate processes scientist and another co-author of the study says:  "This study, together with work we published last year, suggests that there may be a greater role than previously thought for man-made influence on regional climate changes that have profound impacts on society."

This study motivates future international collaborative research because modelling the impact of aerosols is one of the largest uncertainties in climate science – particularly true for aerosol-cloud interactions now being incorporated in the latest generation of climate models.

Taken at face value, this study suggests the number of Atlantic hurricanes over the next couple of decades will depend on future aerosol emissions and how they interact with natural cycles in the North Atlantic. 


This is the actual paper:



The frequency of tropical storms in the North Atlantic region varies markedly on decadal timescales1, 2, 3, 4, with profound socio-economic impacts5, 6. Climate models largely reproduce the observed variability when forced by observed sea surface temperatures1, 8, 10. However, the relative importance of natural variability and external influences such as greenhouse gases, dust, sulphate and volcanic aerosols on sea surface temperatures, and hence tropical storms, is highly uncertain11, 12, 13, 14, 15, 16. Here, we assess the effect of individual climate drivers on the frequency of North Atlantic tropical storms between 1860 and 2050, using simulations from a collection of climate models17. We show that anthropogenic aerosols lowered the frequency of tropical storms over the twentieth century. However, sharp declines in anthropogenic aerosol levels over the North Atlantic at the end of the twentieth century allowed the frequency of tropical storms to increase. In simulations with a model that comprehensively incorporates aerosol effects (HadGEM2-ES; ref. 18), decadal variability in tropical storm frequency is well reproduced through aerosol-induced north–south shifts in the Hadley circulation. However, this mechanism changes in future projections. Our results raise the possibility that external factors, particularly anthropogenic aerosols, could be the dominant cause of historical tropical storm variability, and highlight the potential importance of future changes in aerosol emissions.



The impact of these findings goes way beyond hurricanes. What it is effectively saying is that sea temperatures in the North Atlantic are higher now than they were during the 20thC because of reduced aerosols.

There actually should be little surprise about this. Scientists have long argued that the reduction in NH temperatures in the post-war years was due to aerosols cancelling out the effect of increased levels of CO2.

Yet this sort of air pollution did not begin in 1945. It has been around since the mass industrialisation of the mid 19thC.

How much higher higher would Atlantic temperatures have been 50 or 100 years ago, if concentrations of aerosols had been as low as they are today?

And how much of the rise in land temperatures we have seen in Europe and the US in the last few decades has been due to this aerosol effect?

  1. October 1, 2017 2:30 pm

    Although the theory has an element of credibility, it has exactly the problems that make AGW theory an oversimplified hypothesis dependent upon some computer model that is barely intelligible to the code writers and incorporates all sorts of unprovable correlations.

    In both cases the transmission and absorption of atmospheric gases is at best a crude approximation of reality. The so-called “radiative forcing function” that both depend upon are very crude estimates, yet underpin all predictions.

    They are okay for “what-if” approaches but, even then,should be treated with a large pinch of salt. In fact, none of these theories can be tested in any realistic way: so become a matter of belief in programmers / modellers.

    Given the experience of computer models in the economy, health, weather forecasting etc, it is amazing that they enjoy such world-wide credibility as they do.

    • richard verney permalink
      October 2, 2017 9:09 am

      And it is always a good idea to have a look at some real data, and not simply regard what the model is suggesting is sacrosanct.

      I have set out some real data below which gives some insight into the worth of the Met Office’s claims.

  2. October 1, 2017 2:59 pm

    And not to fossil fuel emissions

  3. October 1, 2017 3:57 pm

    Conceivably also particles and aerosols seeding clouds would perhaps reduce the risks of more sudden and extreme precipitation which built to T.S. or H.
    They might instead create a multitude of smaller storms – dissipating the gathering energy -, rather than allowing one big storm to develop and grow.

  4. October 1, 2017 7:18 pm

    The aerosols can’t stay in position and could be blown anywhere?

  5. Bitter&Twisted permalink
    October 1, 2017 10:01 pm

    So nowt to do with CO2?!

    The authors of this so-called paper are clearly deniers, funded by the fossil fuel industry.

  6. TedL permalink
    October 2, 2017 2:37 am

    There might be another industrial effect on climate, somewhat similar to the effect of aerosols.

    On a couple of blogs have posted unfavorable comments on the idea of a “hydrogen economy” because large amounts of atmospheric hydrogen would in fact be dangerous to the climate. Hydrogen gas leaks easily from pipes and valves. If we were to generate enough hydrogen to actually power a significant part of the economy, so much would leak from containment that it could change the climate and endanger life on earth. Because it is the lightest of gases, hydrogen rises through the atmosphere until it reaches the stratosphere, where it encounters the ozone layer. Ozone is extremely reactive, so it will immediately oxidize the hydrogen, creating water molecules while simultaneously eliminating the ozone. In large amounts one would expect the formation of a layer of ice crystals in the stratosphere, altering planetary albedo, while damaging the ozone layer, which intercepts much of the sun’s UV light.

    I have always thought of this scenario as hypothetical, but I realized a short time ago that maybe we have already experienced this effect. Beginning in the 1850s there was a worldwide adoption of new technology to produce illuminating gas or town gas from coal. Every town of any magnitude in the US had a town gas plant. The composition of town gas was H2, CO and CH4. The pipes and valves used for the gas plants and distribution systems were flanged or threaded, not welded, so H2 gas would have easily escaped. Town gas was gradually replaced by natural gas (CH4) starting in the 1950s. So, for about a century, industrial economies around the world were bleeding large amounts of hydrogen to the atmosphere, presumably with the stratospheric effects mentioned above.

    • accordionsrule permalink
      October 2, 2017 3:07 pm

      That would coincide with the first observance of noctilucent clouds, wouldn’t it?

      • TedL permalink
        October 2, 2017 3:54 pm

        According to the Wikipedia and some other sources on the internet, noctilucent clouds were first reported in 1885. The Wikipedia entry “History of manufactured gas” has the following passage:

        “the rise of the “smoke nuisance” in the 1850s, brought about by the domestic and commercial use of coal, in many cities and metropolises; direct combustion of coal being a particularly notorious source of pollution; which the widespread use of gas could abate, especially with the commencement of using gas for purposes other than illuminating during the 1870s; for cooking, for the heating of dwelling-houses, for making domestic hot water, for raising steam, for industrial and chemical purposes, and for stationary internal combustion engine-driving purposes – which were previously met by employing coal;”

  7. richard verney permalink
    October 2, 2017 8:52 am

    Unfortunately, I have not got up to date data, but the North Atlantic SST has not warmed for 20 years between 1996 and 2016:

    The South Atlantic SST has not risen for some 30 years between 1986 and 2016,

    I am not sure what has happened in 2017, but I rather doubt that there has been much change, especially since many recent papers are reporting a fall in North Atlantic Ocean Heat Content, and suggesting that present day North Atlantic OHC is no more than it was in the 1950s!!! See:

    This is from the Duchez et al 2016 paper and you will note the red plot which is ARGO data. According to ARGO, there has been a very rapid and steep decline in OHC these past 10 years!!!

  8. richard verney permalink
    October 2, 2017 9:05 am

    Further to my recent post above, here is the plot of North Atlantic SST from the recent Reynolds et al 2017 paper:

    From the Chafik et al 2016 paper, once more showing that current North Atlantic SST temperatures are less than they were in the 1950s:

    And from the 2016 de Jong and de Stuer paper which also shows that current SST is no warmer than 1950s, and is cooler than the 1940s and even 1890.

    Whilst i have little regard for the accuracy of historic data, it is interesting that all these recent papers are showing similar trends, namely that the North Atlantic is not currently warm, and has been warmer in the past.

    I take any comment from the Met Office with a pinch of salt. It is not known for its accuracy, and I rather doubt that it has reviewed the recent papers on the North Atlantic.

    • October 2, 2017 7:38 pm

      Great comment. Thank you. I have found that many climate change papers share the peculiar feature of appearing to know but conceding that we don’t really know.

  9. dennisambler permalink
    October 2, 2017 9:13 am

    “However, the relative importance of natural variability and external influences such as greenhouse gases, dust, sulphate and volcanic aerosols on sea surface temperatures, and hence tropical storms, is highly uncertain.”

    So the sudy is meaningless.

    “we assess the effect of individual climate drivers on the frequency of North Atlantic tropical storms between 1860 and 2050, using simulations from a collection of climate models.”

    This is the equivalent of a meta-study in epidemiology, averaging averages.

    “We show that anthropogenic aerosols lowered the frequency of tropical storms over the twentieth century”

    No they haven’t, and they cannot make that claim. They have produced a computer model that shows that possibility, given particular inputs.

    “Our results raise the possibility that external factors, particularly anthropogenic aerosols, could be the dominant cause of historical tropical storm variability, and highlight the potential importance of future changes in aerosol emissions.”

    The key words and phrases are: “raise the possibility”, “could be”, “potential importance”.

    This is not scientific proof of anything. Aerosols are now “linked” to hurrican activity because of yet another computer exercise. The cooling of the 60’s and 70’s has always been explained away by the miraculous appearance of aerosols and presumably their disappearance again, therefore global cooling was really global warming in disguise.

    Extreme weather was more extreme in earlier centuries before industrialisation. This is another attempt to pin the tail on the donkey.

  10. NeilC permalink
    October 2, 2017 10:27 am

    Does anyone esle get “The world must de-industrialise” mantra here. There is no hope!

    When will these people understand computer models are NOT DATA.

    The world has been hotter/colder, wetter/drier, sunnier/darker, stormier/calmer, wetter/drier in the past, but naturally, they will never learn.

  11. Bloke down the pub permalink
    October 2, 2017 10:36 am

    To paraphrase, they couldn’t get their climate models to match reality, so they had to invent some more variables. How does Von Neumann’s quote go, ‘With four parameters I can fit an elephant, and with five I can make him wiggle his trunk’?

    • Bitter&twisted permalink
      October 2, 2017 2:51 pm

      Yup just about says it all.

  12. David permalink
    October 10, 2017 8:04 pm

    I always understood that hydrogen when arriving at the top of the stratosphere would bounce off into space as its electron speed was faster than the earth’s escape velocity. Also why should it combine with ozone without some ‘burning’ process?

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