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Fact-checking the second volume of the U.S. National Climate Assessment

By Roger Andrews | Energy Matters | December 4, 2018

This recently-issued study (the “Assessment”) was seized on by the media as proof of the massive damage the US will suffer if nothing is done about climate change. The Assessment’s conclusions are based largely on speculative model projections that aren’t amenable to checking, but it also claims that the US is already experiencing some of the impacts of man-made climate change, and these claims can be checked. This post accordingly evaluates them claim-by-claim and finds that they are rarely backed up by any hard data, that in some cases they are contradicted by disclaimers buried in the text, and that in no case is there any hard evidence that conclusively relates the impacts to man-made climate change. The credibility of the Assessment’s predictions can be judged accordingly.

The Assessment is 1,600 pages long and I doubt that anyone has read it from cover to cover – I certainly haven’t. I have obtained my information from the Summary Findings, Overview, Report Chapters and Downloads sections in the boxes that clicking on this link leads to. These sections themselves contain several hundred pages of text, much of it repetitive, but there is always the possibility that I’ve missed some critical graphic or piece of text. On the other hand, if I’ve missed it the media, who will have read the introductory sections only, will have too.

And how did the media report the Assessment’s results? Here are some excerpts:

Guardian

Climate change is already harming Americans’ lives with “substantial damages” set to occur as global temperatures threaten to surge beyond internationally agreed limits ……… The influence of climate change is being felt across the US with increases in disastrous wildfires in the west, flooding on the east coast, soil loss in the midwest and coastal erosion in Alaska

CBS News

Billions of hours in productivity will be lost. Hundreds of billions of dollars will be wiped from the economy. Tens of thousands of people will die each year. The scientific report, which was produced by 13 federal agencies, describes an American future nothing short of apocalyptic due to rising threats from climate change …. rising sea levels, disruptions in food productions and the spread of wildfires — have all come true today.

National Public Radio

Climate change is happening here and now …. It is affecting all of us no matter where we live. And the more climate changes, the more serious and even more dangerous the impacts will become.

US News & World Report

From record-breaking wildfires that destroyed more than 14,000 homes in California, to hurricanes that devastated parts of Florida and much of Puerto Rico, long-predicted impacts of climate change are here and wreaking havoc.

The media never lose an opportunity to cast climate change in the worst possible light, or fail to report it when someone else does it for them.

And what are the climate change impacts that the Assessment claims are “happening here and now”, which are the only ones we can verify, or not verify as the case may be, against observations? These excerpts identify them either explicitly or implicitly:

Glaciers and snow cover are shrinking

Increases in greenhouse gases and decreases in air pollution have contributed to increases in Atlantic hurricane activity since 1970.

America’s trillion-dollar coastal property market and public infrastructure are threatened by the ongoing increase in the frequency, depth, and extent of tidal flooding due to sea level rise

Existing water, transportation, and energy infrastructure already face challenges from heavy rainfall, inland and coastal flooding, landslides, drought, wildfire, heat waves, and other weather and climate events

Climate-related changes in weather patterns and associated changes in air, water, food, and the environment are affecting the health and well-being of the American people, causing injuries, illnesses, and death.

Rising air and water temperatures and changes in precipitation are intensifying droughts, increasing heavy downpours, reducing snowpack

Our Nation’s aging and deteriorating infrastructure is further stressed by increases in heavy precipitation events, coastal flooding, heat, wildfires

Some storm types such as hurricanes, tornadoes, and winter storms are also exhibiting changes that have been linked to climate change

After eliminating repetition and sorting the individual impacts into something resembling order we are left with droughts; floods; heavy precipitation; heat waves; wildfires; Atlantic hurricanes; tornadoes; winter storms; sea level rise; glaciers and snowpack; injuries, illnesses and death. We will review these in order of appearance:

1. Droughts

The Assessment begins by claiming that climate-change-induced droughts are intensifying in the US. Then later in the text it shoots itself in the foot:

While there are a number of ways to measure drought, there is currently no detectable change in long-term U.S. drought statistics using the Palmer Drought Severity Index

And adds a graphic to prove it, reproduced below as Figure 1:

Figure 1: US drought conditions. The Palmer Drought Severity Index is the commonly-used metric for measuring drought intensity

2. Floods

The Assessment provides no hard data to back up its claims that climate change is already causing increased flooding in the US (coastal flooding is discussed under sea level rise). The only quantitative historical data I can find on US floods are summarized in Figure 2 (data from Researchgate ):

Figure 2: Two measures of US flood damage, 1934-2000

These graphics don’t tell us whether floods in the US are on the increase or not. And the Assessment doesn’t tell us either, Not only does it fail to detect any nationwide trends, it states that it never claimed any relationship between floods and man-made climate change to begin with:

Analysis of 200 U.S. stream gauges indicates areas of both increasing and decreasing flooding magnitude but does not provide robust evidence that these trends are attributable to human influences …. Hence, no formal attribution of observed flooding changes to anthropogenic forcing has been claimed.

3. Heavy Precipitation

Since the Assessment admits that there are no detectable human-induced trends in US flooding we can reasonably assume that the claimed increase in heavy precipitation events has had no impact. But we will look at the data anyway. The Assessment presents this   graphic to back up its claim that heavy precipitation events are increasing over the US as a whole (Figure 3). As usual, the source of the data is not specified:

Figure 3: Percent of US land area with heavy precipitation events

The U.S. Global Change Research Program, under the auspices of which the Assessment was written, also produces graphics showing how heavy precipitation has changed with time and by region in the US (they may in fact be buried in parts of the Assessment I haven’t looked at). According to Figure 4 (from Globalchange) heavy precipitation events have increased over all of the US except the Southwest:

Figure 4: Increases in US total precipitation and very heavy precipitation events by region

And Huang et al (2017) produce time series showing how total precipitation and extreme precipitation in the Northeast US have both increased since about 1960 (Figure 5):

Figure 5: Increases in US total and extreme precipitation

So in this case the claim checks out against observations, or least in the northeast US. A lingering question, however, is how much of the increase in heavy precipitation was caused by man-made climate change. The Assessment implicitly assumes that all of it was, but a 2015 study by Hoerling et al. concludes that most of the changes after 1979 were caused by ocean variability:

Based on the modeling results, we conclude that anthropogenic climate change has not been a principal factor driving key characteristics of observed changes in U.S. heavy daily precipitation since 1979 …. Our results provide evidence for an alternative argument for another factor that has been operating in recent decades, namely, that statistics of U.S. heavy precipitation have been sensitive to strong decadal ocean variability since 1979

4. Heat Waves

One of the problems with heat waves is defining them (droughts and floods have the same problem). How hot does it have to get, and for how long, before a warm spell becomes a heat wave? The Assessment does not tell us. All it presents in the way of evidence for an increase in heat waves in the introductory report sections, including the 186-page “Report-in-Brief”, is this graphic (Figure 6), which shows the “heat wave season” increasing since the 1960s but not how many heat waves there were. Once again the data source is not specified, nor is the meaning of the cross-hatching:

Figure 6: Length of US “heat wave season”

The next graphic (Figure 7) is another one I added from the globalchange website. It shows an increase in daily record high temperatures in recent decades but again provides no information on the number of heat waves. How many of the record highs, for example, occurred in the winter?

Figure 7: Record daily highs in the US. The meaning of “ratio of daily temperature records” isn’t clear

The only graphic I found that provided any historic information on the incidence of heat waves was the Figure 8 plot of the EPA’s Annual Heat Wave Index. It’s not surprising that it doesn’t appear in the Assessment:

Figure 8: US annual heat wave index since 1895

5. Wildfires

The Assessment provides two graphics to support its claim that climate change is causing more wildfires. Figure 9 shows the first. Again no data source is cited, but it turns out that it comes from the National Interagency Fire Center:

Figure 9: Acres burned by US wildfires since 1987

It also shows only a fraction of the NIFC data. Figure 10, for what it may be worth, shows the complete plot. I say “for what it may be worth” because the plot comes accompanied by this disclaimer:

The National Interagency Coordination Center at NIFC compiles annual wildland fire statistics for federal and state agencies. This information is provided through Situation Reports, which have been in use for several decades. Prior to 1983, sources of these figures are not known, or cannot be confirmed, and were not derived from the current situation reporting process. As a result the figures prior to 1983 should not be compared to later data.

Figure 10: Acres burned by US wildfires. Figure 9 data carried back to 1926

Figure 11 reproduces the Assessment’s second graphic. It shows that about half of the increase in acreage burned was caused by climate change. (Note that it conflicts with the Figure 9 data, according to which a cumulative total of 173 million acres, not 23 million, has been burned since 1984).

Figure 11: Acreage burned by naturally-occurring wildfires vs. acreage burned by climate-change-caused wildfires

In this case the data source is specified. It’s a 2016 paper written by John T. Abatzoglou and A. Park Williams entitled “Impact of anthropogenic climate change on wildfire across western US forests”. How did they segregate climate change-caused wildfires from naturally-occurring wildfires? They used climate models:

We quantify the influence of ACC (anthropogenic climate change) using the Coupled Model Intercomparison Project, Phase 5 (CMIP5) multimodel mean changes in temperature and vapor pressure …. This approach defines the ACC signal for any given location as the multimodel mean 50-y low-pass-filtered record of monthly temperature and vapor pressure anomalies relative to a 1901 baseline.

Before we can accept these results as meaningful we must assume that the global CMIP5 climate models can hindcast temperatures and vapor pressures to a high level of accuracy in the US, which they probably can’t (it’s generally accepted that climate models do a poor job of simulating regional changes). We also have to assume that the numerous other variables that affect wildfires have had no impact. This is a stretch, to put it mildly.

6. Atlantic Hurricanes

In this case the Assessment supplies no data, or at least none that I can find, to back up its claim that Atlantic hurricanes have increased since 1970. So once again I have had to dig up data on my own. Figure 12 (data from the US Environmental Protection Agency) plots the number of North Atlantic hurricanes since 1880. The total number is defined by the orange line, which adjusts for undercounting before 1967, and by the green line after that. There has been an erratic overall increase since about 1970, but since 1880 there has been no clear trend:

Figure 12: Unadjusted hurricane counts, hurricane counts adjusted for undercounting and hurricanes making landfall in the US

The North Atlantic, however, is not part of the US. The important consideration is how many hurricanes have made landfall in the US. These are shown by the red line at the bottom of Figure 12. There is no clear trend since 1970 and if anything a decrease since 1880.

According to Figure 13 (data from Dr. Roy Spencer) major hurricanes making landfall in the US have also been decreasing since the 1930s:

Figure 13: Major hurricanes making landfall in the US

And according to Klotzbach et al (2018) there has been little to no increase in normalized hurricane damages in the US since 1900 (Figure 13):

Figure 14: Normalized damages from hurricanes making landfall in the US

In this case the claim broadly matches observations but conceals (probably deliberately) the big picture, which is that man-made climate change has not increased the incidence of, or the damage caused by, North Atlantic hurricanes making landfall in the US since at least the late 1800s.

7. Tornadoes

Some storm types such as … tornadoes … are also exhibiting changes that have been linked to climate change. Once more the Assessment presents no supporting data, but NOAA’s tornado counts (Figure 15) speak for themselves:

Figure 15: Total tornado and strong-to-violent tornado counts since 1954

8. Winter Storms

… winter storms … are also exhibiting changes that have been linked to climate change.

Once again there are no supporting data in the Assessment, but according to Coleman & Schwartz’s 2017 paper An Updated Blizzard Climatology of the Contiguous United States (1959–2014) the incidence of blizzards in the US has been increasing (Figure 16):

Figure 16: Incidence of blizzards in US

Is this counter-intuitive increase related to climate change? NOAA thinks it may be, although NOAA’s explanation works only in the eastern US ….

Conditions that influence the severity of eastern U.S. snowstorms include warmer-than-average ocean surface temperatures in the Atlantic. These can lead to exceptionally high amounts of moisture flowing into a storm and contribute to greater intensification of the storm. Natural variability can affect ocean surface temperatures, but as global surface temperatures increase, the temperature at any time is higher than it would have been without climate change.

…. and it doesn’t match up very well with trends in sea surface temperatures off the eastern US coast (data from KNMI Climate Explorer) ….

Figure 17: Sea surface temperatures along US east coast (30N-45N, 65W-80W)

… and according to the IPCC Fifth Assessment Report it’s going off in the wrong direction:

Changes in the frequency, severity, and duration of extreme events may be among the most important risks associated with climate change. In some parts of North America, this includes fewer periods of extreme cold, fewer snowstorms ….

Milder winter temperatures will decrease heavy snowstorms .…

This is one of the cases where the claim matches observational changes, but no conclusion as to causation can be reached until there is agreement over whether climate change causes a) more snowstorms, b) fewer snowstorms or c) both at the same time. My money is on c).

9. Sea Level Rise/Coastal Flooding

These are related phenomena, so I will discuss them under the same heading.

Once more there are no supporting data in the Assessment, so once more I had to go searching for some. This graphic from NOAA shows an increase in high-tide flooding that correlates with an increase in “coastal sea level” (Figure 18):

Figure 18: Average days/year with high-tide flooding vs. US sea level

And as shown in Figure 19 (data from EPA) the increased flooding is dominantly an east coast phenomenon:

Figure 19: Average number of tidal floods/year, 2010-2015 vs. 1950-1959

But note the fine print. These are “nuisance floods” that don’t do any serious damage. There is no accepted definition of a nuisance flood, but a maximum water depth of 10cm has been proposed. And a 10cm-deep flood is hardly a catastrophic event.

And what does sea level rise have to do with the increase in nuisance floods? Not much. The reason nuisance floods are more common along the east coast of the US is that the east coast is sinking (a result of glacial rebound*, sediment compaction and groundwater extraction) while the west coast isn’t, and the rate at which the east coast is sinking exceeds the rate at which sea levels are rising in many places. The PSMSL tide gauge record from Sewell’s Point, near the mouth of Chesapeake Bay, is an example (Figure 20). The trend line shows sea level rising at an average rate of 4.5mm/year, but according to the United States Geological Survey less than half of this – maybe less than 2 mm/year – is a result of eustatic sea level rise. The rest is caused by land subsidence:

* Glacial rebound causes the land in and immediately around the ice sheet to rise while the surrounding land, which was squeezed upwards by the ice, sinks back down again. 

Figure Figure 20: Relative sea level rise, Sewell’s Point, Virginia

10 cm nuisance floods and ~2 mm/year sea level rises also pale into insignificance beside the hurricane storm surges that have occurred in the past and which can be expected to recur in the future along the US east coast. They reached heights of eight feet at Sewell’s point during Hurricane Isabel as recently as 2003 and 18 feet along the North Carolina coast during Hurricane Hazel in 1954.

My 2016 post on Isle de Jean Charles, Louisiana describes how sea level rise routinely takes the blame for inundations it didn’t cause. The Assessment cites it as an example of climate change in action.

10. Glaciers and snowpack

North American glaciers have indeed been retreating, as the Assessment claims. But  according to Oerlemans (2005, Figure 21) they have been retreating since about 1825 and retreating rapidly after 1890, well before human-induced climate forcings became significant. This raises the question of whether the retreat has anything to do with man-made climate change:

Figure 21: Glacier retreat since 1700. The green line is North America

No data are available on snowpack, but Rutgers University publishes North American snow cover data (Figure 22). The trend line shows only a very minor decrease since 1975:

Figure 22: Snow-Covered Area in North America, 1972-2015

11. Injuries, Illnesses and Death:

Climate-related changes in weather patterns …. are affecting the health and well-being of the American people, causing injuries, illnesses, and death.

No data on illnesses or injuries are readily available, but over the last ten years approximately 25 million people have died in the US. According to Wikipedia
natural disasters of the type that commonly get blamed on climate change (hurricanes, floods, blizzards, wildfires, tornadoes) have claimed only 1,200 lives over this period.

Conclusion:

In this post I have fact-checked eleven separate climate change impacts which according to the Assessment’s summary sections are already doing damage in the US. In six of these cases (heavy precipitation, heat waves, wildfires, winter storms, sea level rise/coastal flooding and glacier retreat) there is observational evidence – most of which I have had to dig up myself – for impacts that might be related to man-made climate change, but in all of them this evidence is equivocal (e.g. wildfires) or the impacts are insignificant (e.g. nuisance tidal floods). In the other five cases (droughts, floods, Atlantic hurricanes, tornadoes, and injuries, illnesses and deaths) the observational evidence either contradicts the Assessment’s claims or the Assessment admits later in the text that the claim isn’t valid (droughts and floods).

Clearly the Assessment was conducted with little regard for the facts. A disregard for the facts, however, is necessary if one wishes to get the climate change catastrophe message across.

December 4, 2018 - Posted by aletho | Deception, Fake News, Mainstream Media, Warmongering, Science and Pseudo-Science, Timeless or most popular | CBS News, NPR, The Guardian, US News & World Report