Weathering a Storm of Climate Denial

A friend of mine, JP, started all of this when writing:

If you were to ask me 2 years ago what my key understandings were about climate change, I would have said the following:

Sea ice is rapidly shrinking (summer arctic sea ice to be gone by 2015)

Sea levels are rising and accelerating

Polar bear populations are under stress (have increased in the last 20 years)

The levels of glacial retreat around the world are unprecedented (similar retreats have been seen in the last century)

97% of scientists agree that global warming is real and an urgent problem

Any scientist who is skeptical about the claims made about climate change is a "denier" and is funded by oil/resource companies

We are seeing an increase in extreme weather events (they are actually getting less common)

Climate models are accurate in their predictions 

Every one of those things is either totally false, or a largely exaggerated claim.

This is the seventh in a series based on my response, which itself was split over a few emails.  The first was Ice Extent Challenge (in which I provided a little more context about JP) and was followed by Sea Levels Rising, Polar Bears and Climate Change, Glacial Retreat, A Worry of Climate Change Scientists and Denying Denialism.  Some of the issues may also be touched on in a series of articles on the nature of climate denialism.  Please also note the caveat.

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JP’s Claim: The statement “We are seeing an increase in extreme weather events” is either totally false or largely exaggerated and “they are actually getting less common”

There are two factors here which need to be extracted – the frequency of extreme weather events and the severity of extreme weather events.  JP’s parenthetical codicil seems to indicate that it’s a question of frequency while, from my reading, it’s more about severity.

Then there is the question of timing.  Is it merely about historical records, about which you think there would be little controversy?  Or is it about the projections produced by climate modelling?

If it’s related to climate modelling, then we must consider both the accuracy of the models and the accuracy of the data.  It’s quite possible that models, especially earlier models, have been inaccurate in their projection of extreme weather events – underlying assumptions may have been wrong, our understanding of the physics may have been immature, parameterisation may have been too coarse and the data input to the models is unlikely to have been absolutely correct (for instance there will be rounding of datapoints).

In IPCC report AR5 Part A, there is reference to Severe Storms:

Severe storms such as tropical and extratropical cyclones (ETCs) can generate storm surges over coastal seas. The severity of these depends on the storm track, regional bathymetry, nearshore hydrodynamics, and the contribution from waves. Globally there is low confidence regarding changes in tropical cyclone activity over the 20th century owing to changes in observational capabilities, although it is virtually certain that there has been an increase in the frequency and intensity of the strongest tropical cyclones in the North Atlantic since the 1970s (WGI AR5 Section 2.6). In the future, it is likely that the frequency of tropical cyclones globally will either decrease or remain unchanged, but there will be a likely increase in global mean tropical cyclone precipitation rates and maximum wind speed (WGI AR5 Section 14.6).

Note that this IPCC report is a key reference document with respect to climate change.  It basically collates evidence from 9200 peer-reviewed studies and concludes that climate change is happening, that climate change is due to human activity and that the effects of climate change (both current and future) are worth worrying about.  Per Wikipedia, the principal findings were:

General

·        Warming of the atmosphere and ocean system is unequivocal. Many of the associated impacts such as sea level change (among other metrics) have occurred since 1950 at rates unprecedented in the historical record.

·        There is a clear human influence on the climate

·        It is extremely likely that human influence has been the dominant cause of observed warming since 1950, with the level of confidence having increased since the fourth report.

·        IPCC pointed out that the longer we wait to reduce our emissions, the more expensive it will become.

Historical climate metrics

·        It is likely (with medium confidence) that 1983–2013 was the warmest 30-year period for 1,400 years.

·        It is virtually certain the upper ocean warmed from 1971 to 2010. This ocean warming accounts, with high confidence, for 90% of the energy accumulation between 1971 and 2010.

·       It can be said with high confidence that the Greenland and Antarctic ice sheets have been losing mass in the last two decades and that Arctic sea ice and Northern Hemisphere spring snow cover have continued to decrease in extent.

·        There is high confidence that the sea level rise since the middle of the 19th century has been larger than the mean sea level rise of the prior two millennia.

·        Concentration of greenhouse gases in the atmosphere has increased to levels unprecedented on earth in 800,000 years.

·        Total radiative forcing of the earth system, relative to 1750, is positive and the most significant driver is the increase in CO
2's atmospheric concentration.

Models

AR5 relies on the Coupled Model Intercomparison Project Phase 5 (CMIP5), an international effort among the climate modeling community to coordinate climate change experiments. Most of the CMIP5 and Earth System Model (ESM) simulations for AR5 WRI were performed with prescribed CO2 concentrations reaching 421 ppm (RCP2.6), 538 ppm (RCP4.5), 670 ppm (RCP6.0), and 936 ppm (RCP 8.5) by the year 2100. (IPCC AR5 WGI, page 22).

·        Climate models have improved since the prior report.

·        Model results, along with observations, provide confidence in the magnitude of global warming in response to past and future forcing.

Projections

·        Further warming will continue if emissions of greenhouse gases continue.

·        The global surface temperature increase by the end of the 21st century is likely to exceed 1.5 °C relative to the 1850 to 1900 period for most scenarios, and is likely to exceed 2.0 °C for many scenarios

·        The global water cycle will change, with increases in disparity between wet and dry regions, as well as wet and dry seasons, with some regional exceptions.

·        The oceans will continue to warm, with heat extending to the deep ocean, affecting circulation patterns.

·        Decreases are very likely in Arctic sea ice cover, Northern Hemisphere spring snow cover, and global glacier volume

·        Global mean sea level will continue to rise at a rate very likely to exceed the rate of the past four decades

·        Changes in climate will cause an increase in the rate of CO2 production. Increased uptake by the oceans will increase the acidification of the oceans.

·        Future surface temperatures will be largely determined by cumulative CO2, which means climate change will continue even if CO2 emissions are stopped.

The summary also detailed the range of forecasts for warming, and climate impacts with different emission scenarios. Compared to the previous report, the lower bounds for the sensitivity of the climate system to emissions were slightly lowered, though the projections for global mean temperature rise (compared to pre-industrial levels) by 2100 exceeded 1.5 °C in all scenarios.

The IPCC report is by no means a climate denial document, but even so, it states that the number of tropical cyclones (including hurricanes and typhoons, which are basically the same thing in a different geographical location) will either decrease or stay the same and it’s only the severity that might increase, with increased global mean windspeed and precipitation rates.  The only quantitative statement I could find on cyclones was this (page 247): “In the tropics, the intensity of cyclones is projected to increase 2 to 11% by 2100, which may increase soil erosion and landslides (Knutson et al., 2010).”  Given the timescale involved, it would be unsurprising if there was little or no indication of an increase in cyclone severity in the recent past.

It should be noted that cyclones have a maximum potential intensity and thus a maximum windspeed (about 100 m/s or 360 km/hr), but so far the top speed measured was 345 km/hr in 2015.  (Prior to that, the record was 305 km/hr in 1980.)

Therefore, even if the ocean is warming and that provides more energy to spin up cyclones, then there’s still going to be an upper limit.   It would be reasonable think though that a warmer ocean would power a storm for a longer period and a greater proportion of storms would reach Cat 5.

There is a problem associated with assessing the number and severity of storms, related to the news cycle.  The whole world will hear about a storm that affects the US for days, but rarely will we hear anything about any storm that wipes out small, remote islands without a large tourist trade.  The Union of Concerned Scientists did however report an increase in hurricane activity in the North Atlantic:

Note that there is a downwards trend for hurricanes that reach the US.  The total number of hurricanes appears to be about even (on average) or perhaps increasing, but only by a little.  The data there says nothing about strength though, or duration of the storms.  The same organisation reports that there does not seem to be an increase in hurricane activity across the world, with about 90 per year, mostly in the Pacific.  NOAA report basically no change in the number of storms and their models predict fewer storms, but these storms would produce more precipitation, they would be more intense and more of them would be Cat 4 or 5.  This is also a bit hard to track, I don’t know if they bother recording a storm if it doesn’t reach land, but I am going to go out on a limb and say that they pretty much all do (reach land that is because a cyclone just keeps getting stronger while over a warm sea and will only lose power if it ends up over land or cooler water).

Looking at the records for the Atlantic, there were 2 Cat 5 in the 1950s,  (6 in the 1930s, but there don’t seem to be records for the 40s), 4 in the 60s, 3 in the 70s, 3 in the 80s, 2 in the 90s, 8 in the 00s, and 6 in the 10s.  They seem to be getting stronger, with 5 out of 6 being at 280km/hr or less in the 30s and 4 out of 5 being 280km/hr or more in the 10s, the most recent being 295km/hr (beaten only by Allen in 1980).  There’s an oddity in that in the past, there is a correlation between pressure and top windspeed, generally the lower the pressure, the faster the wind – but in the 2010s, all of the storms had higher pressures despite the wind being fast (recent slower storms were all quite short lived as a Cat 5, half an hour, three hours and six hours – these were basically ambitious Cat 4 hurricanes that didn’t really have the legs to become a proper Cat 5).

I don’t know whether there is enough data there to make any conclusions.  But if we look at Cat 4 hurricanes (in the Atlantic), we see:

Which does seem to have a distinct trend to it.  If we did something similar with Cat 5s, it would look like this:

Which again appears to have something like a trend to it.

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Going back to JP, it was claimed that the statement “We are seeing an increase in extreme weather events” is either totally false or largely exaggerated and “they are actually getting less common”.

This just does not seem to be true.  There appears to be about the same number of severe storms, cyclone or hurricanes, but there is a distinct increase in the number of both Cat 4 and Cat 5 cyclones.  NOAA reports “that, after adjusting for such an estimated number of missing storms, there remains just a small nominally positive upward trend in tropical storm occurrence from 1878-2006. Statistical tests indicate that this trend is not significantly distinguishable from zero.”   They conclude: “In short, the historical Atlantic hurricane frequency record does not provide compelling evidence for a substantial greenhouse warming-induced long-term increase.”  That would indicate that the increase in Cat 4 and Cat 5 storms is at the expense of less intense storms, or rather those storms that do happen are more likely to be intense.

This, in any rational interpretation, means that we are seeing an increase in number of extreme weather events and, on average, weather events are becoming more extreme – although it is conceded that the number of weather events themselves are not necessarily increasing in number.

Therefore, with regard to weather events, the evidence does not support JP’s claim.