Science Snippets: Megadrought Driven by Our Collective Actions

Draft script:

I’ve mentioned our collective actions many times in this space. I am simply trying to clarify that, as individuals, we are not responsible for the bad news I relay. We were all born into a set of living arrangements over which we had no control. Furthermore, a person acting contrary to this set of living arrangements will find him- or herself as an outcast within a very short period of time.

An article published at Colorado Newsline on 18 August 2025 provides an example of our collective actions. Titled Human emissions driving Colorado River ‘megadrought,’ CU Boulder research finds, the article was published 18 August 2025. Here’s the subhead: “Global warming is stalling a key Pacific Ocean climate cycle, reducing Western rainfall.”

Here’s the lede, which comprises the opening paragraph: “As historic drought conditions on the Western Slope fuel another dangerous wildfire season, a new paper from researchers at the University of Colorado Boulder warns that human-caused climate change is playing a major role in making those conditions worse.”

The next paragraph introduces a peer-reviewed paper while placing the blame squarely on the shoulders of humans: “Previously published climatological research has found that the Colorado River Basin’s current ‘megadrought’ is the worst dry spell the region has experienced in at least 1,200 years. But a new study, published last week in the journal Nature, concludes that those persistently dry conditions are being driven by human activity ‘more intensely — and more directly — than previously understood, its authors say.’”

I will quote from the peer-reviewed paper in the renowned journal Nature shortly. Paragraphs four, five, seven, and eight of the story at Colorado Newsline provide necessary context: “Their findings concern a climate pattern known as the Pacific decadal oscillation. Related to the better-known El Niño-La Niña cycle to the south, the … [Pacific Decadal Oscillation] is a natural fluctuation that brings warm water to the northeastern Pacific Ocean near the U.S. West Coast during its ‘positive’ phase, leading to more storms and higher-than-average rainfall. During its ‘negative’ phase, however, cooler water and air temperatures result in less precipitation in Western states.

Despite typically reversing itself every one or two decades, the … [Pacific Decadal Oscillation] has been ‘stuck’ in the negative, dry phase since the 1990s. By analyzing more than 500 climate model simulations developed by climatologists around the world, the study’s authors were able to paint the clearest picture yet of the influence of human activity on the … [Pacific Decadal Oscillation], and the resulting Southwestern megadrought.

Severe drought conditions have persisted in the Colorado River Basin since 2000, putting increased stress on the water supplies relied on by about 40 million people in Colorado and six other Western states. Water levels in two key reservoirs, Lake Mead and Lake Powell, have fallen to record lows in recent years.

Rising levels of greenhouse gases, mostly the result of fossil-fuel combustion, have caused much of western Colorado and neighboring states in the Colorado River’s Upper Basin to warm by an average of more than 4 degrees Fahrenheit above pre-industrial levels, according to National Oceanic and Atmospheric Administration data.” Warming “by an average of more than 4 degrees Fahrenheit above pre-industrial levels” translates to more than 2.2 degrees Celsius. This is not surprising, considering Earth eclipsed the 2 C Rubicon in October 2023, according to governments of the world. In addition, the interior of large continents generally warm faster than the global average.

Near the end of the story in Colorado Newsline come two critical paragraphs: “Colorado and other states that are parties to the 103-year-old Colorado River Compact have negotiated for years over how to distribute the cuts to water use made necessary by the basin’s ongoing drought. The federal Bureau of Reclamation … announced another year of reduced water allocations for the Lower Basin states of Arizona and Nevada.

Not long ago, the possibility that the Pacific decadal oscillation would eventually reverse itself offered hope that the long-term drought outlook for the U.S. Southwest wasn’t as bad as it seemed. Instead, evidence now suggests the last two decades are the region’s ‘new normal.’”

One of the authors of the peer-reviewed paper in Nature provides the bottom line of the article at Colorado Newsline: “That’s the most important implication of our findings. That this drought is here to stay, unless we do something about rising temperatures and global warming.” As you know, there is little we can do about rising temperatures and global warming. Reducing greenhouse gas emissions invokes the aerosol masking effect, among the fastest paths to the extinction of all life on Earth.

I turn now to the peer-reviewed paper in Nature. The Abstract quotes additional peer-reviewed papers in telling the terrible story: “The Pacific decadal oscillation …—the leading pattern of climate variability driving changes over the North Pacific and surrounding continents—is now thought to be generated by processes internal to the climate system. According to this paradigm, the characteristic, irregular oscillations of the … [Pacific Decadal Oscillation] arise from a collection of mechanisms involving ocean and atmosphere interactions in the North and tropical Pacific. Recent variations in the coupled ocean–atmosphere system, such as the 2015 El Niño, ought to have shifted the … [Pacific Decadal Oscillation] into its positive phase. Yet, the PDO has been locked in a consistent downward trend for more than three decades, remanding nearby regions to a steady set of climate impacts. Here we show that the main multidecadal variations in the … [Pacific Decadal Oscillation] index during the twentieth century, including the ongoing, decades-long negative trend, were largely driven by human emissions of aerosols and greenhouse gases rather than internal processes. This anthropogenic influence was previously undetected because the current generation of climate models systematically underestimate the amplitude of forced climate variability. A new attribution technique that statistically corrects for this error suggests that observed … [Pacific Decadal Oscillation] impacts—including the ongoing multidecadal drought in the western United States—can be largely attributed to human activity through externally forced changes in the … [Pacific Decadal Oscillation]. These results indicate that we need to rethink the attribution and projection of multidecadal changes in regional climate.”

The results are surprising, at least to me: “… we need to rethink the attribution and projection of multidecadal changes in regional climate.” As indicated by the designed-to-fail Intergovernmental Panel on Climate Change, Earth is amid the most rapid warming event in planetary history. This event is irreversible. People paying attention to reports from the IPCC have known about the abrupt, irreversible nature of ongoing climate change for more than six years. That impacts are being revealed at regional levels, including in the Colorado River Basin, comes as no surprise.