I’ve been in a few tweet engagements today and have realised that I could now count as a believer in “man-made warming” – although whilst there is still no evidence that could anywhere confirm CO2 induced warming, the evidence does now strongly (overwhelmingly?) point to the reduction in pollution after the 1970s clean air acts. (EAIW or Environmental Action Induced Warming)
As I show below 92% of the evidence is incompatible with CO2 warming. In contrast, 91% of the evidence is compatible with pollution reduction as a cause of the observed warming.
For more detail of pollution reduction as a cause of warming see:
- Understanding Global temperatures X – 1970s Global cooling and 2000s Pause
- CO2 was not cause of Global Warming between 1979-1993
Table
| Effect | Increase in CO2 induced warming | Reduction in cooling inducing Pollution |
| 20th century increase in temperature | The slow warming is typical within available datasets. This does not rule of CO2 warming COMPATIBLE |
There was a general reduction in the level of pollutants over US and Europe.COMPATIBLE |
| Regional hotspots like the Arctic have warmed or Arctic ice disappearing – but Antarctic ice has been increasing | CO2 is well spread geographically. As such warming ought to be similarly well spread. Regional warming is incompatible with CO2 hypothesisINCOMPATIBLE | The main pollution areas were in the US and Europe. Trade winds particularly from the US used to take pollution into Arctic causing coolingCOMPATIBLE |
| There was modest cooling in the 1970s | There has been a steady rise in CO2. Therefore there was no reduction in CO2 that can explain this cooling by CO2INCOMPATIBLE? | The level of pollution rose to a peak in 1970. The 1970s cooling is compatible with air pollution.COMPATIBLE |
| There was a sharp rise in temperature 1970-2000 | There is no similar sharp rise in CO2 in this period. As such CO2 cannot explain why there was relatively rapid warming in this period.INCOMPATIBLE | There was a sharp decrease in air pollutions following the 1970s clean air acts.COMPATIBLE |
| Global warming slowed in 2000. | This cannot be explained by CO2 as it continued to rise.INCOMPATIBLE | Whilst there was rapid reduction in air pollution from the 1970s. Around 2000 the benefits of these measured reduced because there was not much left to clean up.COMPATIBLE |
| The trend from 1985 shows warming hotspots 3-8days downwind of major 1970s polluting areas like US and Europe. | This is incompatible with CO2 warming which should be uniformly spread over globe over long periodsINCOMPATIBLE | This is very compatible with warming caused by the reduction in pollution in these areas.COMPATIBLE |
| Tropopause pressure has reduced. | Warming should cause whole atmosphere to expand. If Troposphere remains at fixed height pressure will increase. Otherwise we expect no change.INCOMPATIBLE | The lowering of Tropospheric pressure is compatible with an overall cooling atmosphere and tropopause staying at same heightCOMPATIBLE? |
| The rate of “pan evaporation” or Global Dimming has fell all over the world except in a few places where it has increased. The trend reversed about 1990 | This is incompatible with global warming because a warmer atmosphere should increase evaporationINCOMPATIBLE | Pollution will increase cloud intensity and reduce pan evaporation. However we would expect slightly earlier reduction and more localised. So, although partly fits without total agreement:INCOMPATIBLE? |
| Increased tropical convection responding to warming sea surface temperatures (SSTs) is supposed to cause enhanced warming in the upper troposphere. | The lack of a tropical hotspot in upper troposphere is strong evidence against CO2 warmingINCOMPATIBLE | Pollution tends to retained in the lower atmosphere until washed out by rain. This causes cooling when present (thus warming when removed). The effect should be in the lower atmosphere as has been found.COMPATIBLE |
| Warming in N.Hemisphere | Warming should be globalINCOMPATIBLE | The main 1970s polluting areas were in the N.Hemisphere.COMPATIBLE |
| Land based metrics warmed much faster than sea | Warming should be globalINCOMPATIBLE | The main 1970s polluting areas were on land – and winds particularly in Europe were over land.COMPATIBLE |
| The climate models fail to predict climate | The models include large positive feedbacks in order to match the 1970-2000. But this means they fail after 2000 when warming paused.INCOMPATIBLE | NA |
| Reduction in Hurricanes | ? | ? |
| Result | Incompatible: 11Compatible: 192% Incompatible | Incompatible: 1Compatible: 1091% compatible |
Conclusion
There is very little reason to suggest that CO2 is the predominant cause of recent climate change and extremely good reason to believe that first the cooling effect of air pollution and then the warming effect of the reduction of air pollution as a result of clean air legislation in the 1970s, and finally the steady state when further clean up was difficult is a very good explanation for most recent climate change. That does not necessarily mean it is the only cause, but it certainly is a strong first contender.
Addendum: I’ve had a complaint that regional warming is not incompatible with CO2 warming. The strict answer is that if you say that CO2 is the main cause of warming and the warming is regional, then it is incompatible. if however, CO2 warming is “buried in the noise” – then it is not. So, perhaps “incompatible with being the only or vast majority cause”
Longterm Effects over Ice-age Cycle
| Effect | Increase in CO2 induced warming | Reduction in cooling inducing Pollution |
| General warming and cooling of Ice-age | CO2 changes and ice-age temperature cycles show a good correlation.COMPATIBLE | INCOMPATIBLE |
| Timing of CO2 and warming | Changes in CO2 LAG changes in temperature suggesting that CO2 changes are being caused by temperature changesINCOMPATIBLE | INCOMPATIBLE |
| At various times there are periods of relatively short term cooling. | These periods of short term cooling lasting a few thousand years often do not have a similar change in CO2INCOMPATIBLE? | INCOMPATIBLE |
| Over very long geological times of 100s of millions of years | there is no correlation between CO2 and temperature. INCOMPATIBLE |
INCOMPATIBLE |
Conclusion
Both CO2 and air born pollution are extremely poor at explaining long term geological climate change with CO2 being slightly better than appalling.
