comparison of drought and green

ABC News is promoting the false claim that human climate change is responsible for a “Mega-drought” affecting much of the Western United States. Although drought conditions have persisted for a couple of years now across portions of the Western United States, droughts in the dry West are common and research shows much larger, longer-term droughts have occurred there historically. Because current conditions are not outside the historic records of drought, there is no evidence human greenhouse gas emissions are contributing the current drought.

In a story, titled “‘Mega-drought’ in West directly linked to climate change, experts say,” ABC New claims,

“The ‘mega-drought’ that’s plaguing much of the western U.S. is a direct consequence of warming global temperatures, according to experts. The term is used to describe a severe and intense drought that spans a couple of decades, National Oceanic and Atmospheric Administration meteorologist Brad Pugh told ABC News.”

ABC News’ report starts from a false premise, that the Western United States has been suffering severe drought conditions for couple of decades. It hasn’t. At worst, some areas of the Western United States have been experiencing some level of drought for a couple of years at most. Data shows “back to back” dry years are not unusual in Western United States, and consecutive years of drought don’t count as a mega-drought, regardless of the severity.

The U.S. Environmental Protection Agency (EPA) reintroduced its Climate Change Indicator series in mid-May. The agency’s post, titled “Climate Change Indicators: Drought,” reported no cause for alarm that climate change is increasing drought. The data cited and graphed by EPA shows no trend towards greater numbers of droughts or droughts of greater severity.

“Average drought conditions across the nation have varied over time,” writes EPA. “The 1930s and 1950s saw the most widespread droughts, while the last 50 years have generally been wetter than average [see the figure below]. Over the entire period … the overall trend has been toward wetter conditions,” wrote EPA.

Figure 1 shows annual values of the Palmer Drought Severity Index, averaged over the entire area of the contiguous 48 states. Positive values represent wetter-than-average conditions, while negative values represent drier-than-average conditions. A value between -2 and -3 indicates moderate drought, -3 to -4 is severe drought, and -4 or below indicates extreme drought. The thicker line is a nine-year weighted average.

Figure 1: Annual values of the Palmer Drought Severity Index, averaged over the entire area of the contiguous 48 states from 1890 to 2020. Posted on EPA Website, Data source: NOAA, 2017 Web update: April 2021

EPA’s drought climate change indicator confirms what other sources of data have shown. As reported in Climate at a Glance: Drought, for example, the United Nations Intergovernmental Panel on Climate Change (IPCC) reports with “high confidence” that precipitation has increased over mid-latitude land areas of the Northern Hemisphere (including the United States) during the past 70 years. IPCC also has “low confidence” about any negative precipitation trends occurring globally.

Moreover, the U.S. National Oceanic and Atmospheric Administration reports America is currently is undergoing its longest period in recorded history with less than 40 percent of the country experiencing “very dry” conditions. Also, the United States in 2017 – and then again in 2019 – registered its smallest percentage of land area experiencing drought. Indeed in 2019, California, which is currently suffering under widespread and severe drought conditions, just two short years ago experienced among its wettest years since official records have been kept.

Conditions in Colorado and Wyoming also show how mistaken ABC News’ claims of a Western mega-drought are. Although nearly 2/3 of Colorado was experiencing severe drought or worse in June of 2020, and 93 percent of the state was suffering “severe drought” or worse as of January 2021. Yet, currently more than half the state is experiencing no drought at all, and just 35 percent of the state is experiencing severe drought or worse.  In naturally arid Wyoming, one year ago, nearly 99 percent of Wyoming was entirely drought-free. This has changed. At present, 68 percent of Wyoming is suffering from some level of drought, with 24 percent experiencing at least severe drought. The data from Colorado and Wyoming’s demonstrate how dramatically precipitation conditions can change in short periods of time.

Going back further in time, research conclusively demonstrates the current drought in the Western United States is not historic in length or severity. It is well-recognized that drought is cyclical, and mega-droughts, some lasting 100 years or more, have been commonplace in the past.

In the book “The West Without Water,” the authors wrote,

“Prolonged droughts — some of which lasted more than a century — brought thriving civilizations, such as the ancestral Pueblo (Native Americans) of the Four Corners region, to starvation, migration and finally collapse.”

Indeed, research shows decade-long droughts happen once or twice a century in the Western United States, and droughts last for multiple decades, occur a few times each millennium. In a 2016 Columbia University Academic Commons paper, the authors’ state,

“During the Medieval Climate Anomaly (MCA), Western North America experienced episodes of intense aridity that persisted for multiple decades or longer. These mega-droughts are well documented in many proxy records, but the causal mechanisms are poorly understood.”

In short, contrary to ABC News’ report, the Western United States is not in the midst of a two decade long mega-drought, and it is impossible to attribute current drought conditions, only two years old, to human caused global warming.




H. Sterling Burnett, Ph.D., is the Director of the Arthur B. Robinson Center on Climate and Environmental Policy and the managing editor of Environment & Climate News. In addition to directing The Heartland Institute's Arthur B. Robinson Center on Climate and Environmental Policy, Burett puts Environment & Climate News together, is the editor of Heartland's Climate Change Weekly email, and the host of the Environment & Climate News Podcast.


  1. “Large contribution from anthropogenic warming to an emerging North American megadrought”

    Severe and persistent 21st-century drought in southwestern North America (SWNA) motivates comparisons to medieval megadroughts and questions about the role of anthropogenic climate change. We use hydrological modeling and new 1200-year tree-ring reconstructions of summer soil moisture to demonstrate that the 2000–2018 SWNA drought was the second driest 19-year period since 800 CE, exceeded only by a late-1500s megadrought. The megadrought-like trajectory of 2000–2018 soil moisture was driven by natural variability superimposed on drying due to anthropogenic warming. Anthropogenic trends in temperature, relative humidity, and precipitation estimated from 31 climate models account for 46% (model interquartiles of 34 to 103%) of the 2000–2018 drought severity, pushing an otherwise moderate drought onto a trajectory comparable to the worst SWNA megadroughts since 800 CE.”


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