By James D. Agresti
February 4, 2016
In a recent article about global warming adorned with pictures of flooding and drought, New York Times environmental journalist Justin Gillis wrote:
A warmer atmosphere can hold more water vapor, and an intensification of rainstorms was one of the fundamental predictions made by climate scientists decades ago as a consequence of human emissions. That prediction has come to pass, with the rains growing more intense across every region of the United States, but especially so in the East.
Gillis did not provide a source, timeframe, or data to support these assertions, so Just Facts contacted him to request this information. He replied by pointing to a 2013 report by the Intergovernmental Panel on Climate Change (IPCC) and to the Obama administration’s National Climate Assessment (NCA).
The IPCC’s internal documents show that it has engaged in deceitful actions to exaggerate global warming, which suggests that its findings should not be uncritically accepted. However, even when taking this IPCC report at face value, it does not prove Gillis’ claim. Instead, it states that the evidence for changes in rainfall intensity is equivocal and varying:
[S]ince 1951 there have been statistically significant increases in the number of heavy precipitation events (e.g., above the 95th percentile) in more regions than there have been statistically significant decreases, but there are strong regional and sub-regional variations in the trends. In particular, many regions present statistically non-significant or negative trends, and, where seasonal changes have been assessed, there are also variations between seasons (e.g., more consistent trends in winter than in summer in Europe).
Looking judiciously at these IPCC findings, the evidence becomes even murkier. This is because apparent changes in rainfall intensity sometimes vanish when examining longer timeframes that better account for natural variations. For example, in 2015, the International Journal of Climatology published a paper about extreme rainfall in England and Wales that revealed: “Contrary to previous results based on shorter periods, no significant trends of the most intense categories are found between 1931 and 2014.”
A similar situation exists with average rainfall, which differs from rainfall intensity in that it measures total rainfall instead of the portion of rain that occurs in heavy downpours. In 2015, the Journal of Hydrology published a study of “over 1½ million monthly precipitation totals observed at 1000 stations in 114 countries.” The study found:
- “No significant global precipitation change from 1850 to present.”
- “Many stations experienced increased precipitation during one period but decreased precipitation during another time period.”
- Previous major studies of rainfall patterns analyzed “a few decades of data” and produced “conflicting” outcomes, which is “not entirely surprising given that precipitation varies considerably over time scales of decades.”
These facts all drive home the importance of looking at the broadest possible range of evidence instead of cherry picking selected time periods or areas. Flouting this tenet of honest science, Gillis focused on the United States without mentioning that it has the strongest rainfall intensity trends on the planet. According to the IPCC, central North America (i.e., the U.S.) has “the overall most consistent trends towards heavier precipitation” of any region in the world.
Since rainfall trends vary widely by area, and since the United States contains only 1.9% of the world’s surface area, Gillis’ statement about rainfall in the U.S. amounts to an anecdote. Yet even in this “worst case” example, the feared effect of greater flooding was not confirmed by a rigorous study of U.S. flood trends published in Hydrological Sciences Journal.
To conduct this study, scientists analyzed data from 200 water gauges with records extending from 85 to 127 years ago. To eliminate the effects of land development, the data was gathered from gauges located on streams far from man-made structures like reservoirs and parking lots. The study found “no strong empirical evidence” for increased flood magnitudes across any of the four major regions of the United States. In one of these regions (the Southwest), the study actually found a decrease in flooding, and in another region (the Northeast), the study found results that are “suggestive” of increased flooding but not statistically significant.
Nonetheless, Gillis’ New York Times article and the Obama administration’s NCA displayed images of floods as if they were caused by extreme rainfall from global warming. The NCA also stated, “There has also been an increase in flooding events in the Midwest and Northeast where the largest increases in heavy rain amounts have occurred.”
The source that the NCA cites for that claim, a 2013 paper in the Bulletin of the American Meteorological Society, provides no proof that more intense rain has increased flooding anywhere in the United States, much less any evidence that the rain was caused by global warming. With reference to a few areas of increased flooding, the paper notes that “land management practices” and “oscillatory behavior at a time scale on the order of a century” may be contributing factors. With regard to the East, which is the area with the greatest rise in rainfall intensity, the paper notes:
Days with heavy precipitation have been increasing significantly across the eastern United States, particularly in New England (Karl et al. 2009; Kunkel et al. 2013). Interestingly, this trend is not strongly related to changes in river flooding.
In spite of these facts, when the Obama administration released its NCA in 2014, the New York Times published an article entitled “U.S. Climate Has Already Changed, Study Finds, Citing Heat and Floods.” This piece was also authored by Gillis, and he wrote that “in recent years, sudden intense rains have caused extensive damage.” He then listed three instances of floods with the clear implication that these events were caused by global warming.
The New York Times claims to abide by “Standards and Ethics” that require its staff to tell “the complete, unvarnished truth as best we can learn it.” These standards also declare that “the journalism we practice daily must be beyond reproach,” and the organization has “an ethical responsibility to correct all its factual errors, large and small.” More than a week has passed since Just Facts sent Gillis most of the information above, and the Times has not issued a correction.
A growing number of environmental advocates, journalists, and scientists have misrepresented evidence concerning the effects of global warming. This is typically done in conjunction with efforts to hinder people from using sources of energy that produce more greenhouse gases and toxic pollutants. However, these energy sources generally have lower costs than other forms of energy, and inexpensive energy is essential for public health and economic progress, particularly for the world’s poorest people. Hence, there is a continual debate over the pros and cons of various forms of energy.