As we saw in earlier installments of this series, President Donald Trump and former Vice President Joe Biden have starkly different takes on what to do about human-produced climate change over the next four years. One thing is clear: Whichever one gets the nod in the Nov. 3 election will face a daunting landscape of impacts and an increasingly compressed time frame for action. Much of what we can expect over the next four years in both weather impacts and climate research is already evident, both globally and regionally.

Two types of climate-linked disaster have surged to the forefront of public consciousness during the Trump administration: fires and floods. Californians were pummeled by a string of catastrophic fires starting in 2017, including the state’s largest, deadliest, and most destructive blazes in modern records. Disastrous fires also struck Oregon and Washington in the summer of 2020, and Colorado’s three largest wildfires on record raged from late summer well into autumn 2020.

The common thread in these events is intense windstorms blowing through heat-dessicated landscapes. The climate of the West is famously drought-prone, and occasional windstorms are familiar, but the relentless rise of regional temperatures – proceeding even faster than nationwide warming in recent decades – has made the atmosphere in a given drought even “thirstier.” Record-hot readings during the naturally arid California summer can now lead to record-dry trees, shrubs, and grasses by late summer and autumn, even in some years that had ample winter moisture, such as 2016-17.

To make matters worse, increasingly late onsets of winter moisture are prolonging the state’s fire season. Extreme fire-weather days in autumn have more than doubled over the past 40 years, according to a recent study, and California’s wet season may be increasingly pinched on either end as climate change unfolds.

Meanwhile, the Atlantic and Gulf coasts and Puerto Rico have been ravaged by five major hurricane landfalls since Trump was elected, starting with Harvey’s catastrophic hit and the resulting epic rainfall and flooding in Texas in August 2017. This year has seen a record 11 named storms make U.S. landfalls, including Hurricane Zeta in storm-weary Louisiana on Oct. 27.

It’s the vagaries of week-to-week and year-to-year weather patterns that determine which storms move inland or stay out to sea. However, the overall frequency of major hurricanes in the Atlantic has jumped since the 1990s, a trend linked to climate change in a number of studies.

Moreover, warming oceans are pumping ever more moisture into the atmosphere, which helps make it easier for landfalling hurricanes – especially slow movers like Harvey, which are becoming more common with climate change – to deposit more rain. Hurricane Florence’s winds had dropped to Category 1 strength by the time the hurricane reached North Carolina in September 2018, but as Florence dragged its heels near the coast, it produced more than $20 billion in damage, most of it from flooding.

Colliding catastrophes

If Zeta turns out to be a billion-dollar storm, it will make the nation’s estimated inflation-adjusted toll from fires, floods, and other billion-dollar weather disasters from 2017 to 2020 – already at $510.7 billion – the highest for any four consecutive years in data going back to 1980, according to the National Oceanic and Atmospheric Administration. There’s no particular reason to expect the toll to plummet over the next four years. If anything, say the experts, parallel catastrophes may compete even more for our attention and our money.

“Just think about the extreme weather disasters we’ve seen in recent years,” said climate scientist Michael Mann of Pennsylvania State University. “We can expect these events to become more frequent and more extreme as long as we continue to release carbon pollution into the atmosphere.”

At Texas Tech University, climate scientist Katharine Hayhoe is also concerned about the rising risk in the 2020s of “multiple extreme and very damaging events that are obviously beyond what would normally be expected and clearly super-sized by a changing climate.”

One major research area over the last decade has been climate-change attribution science – or, as Hayhoe puts it, “how much more likely, or stronger, or longer, or more damaging did climate change make a given event?”

A running series of papers in the Bulletin of the American Meteorological Society has analyzed a wide range of specific weather events, assessing the extent to which human-produced climate change could have made each one more likely. Out of 168 studies covering events from 2011 to 2018, almost three-quarters found a climate-change connection. Several events – all related to heat – were deemed virtually impossible without the hand of fossil fuel emissions.

A separate study published in April, using a new analysis technique, found that about three-quarters of the estimated $90 billion cost of Harvey can be traced back to the enhancement of the hurricane’s rains by warmer oceans.

“I think we’re going to see some big lawsuits in future years as this science evolves further, and as climate change continues to load the dice against us and the tide turns against the big emitters,” said Hayhoe.

As climate researchers drill down to specific types of weather events related to global climate change, they’re guided by increasingly detailed regional-scale models that can be nested within global climate simulations. Global models are generally too coarse in scale to capture events such as hurricanes or thunderstorm complexes, but an increasing number of regional models can do just this. The idea isn’t to predict where, say, a Hurricane Xanadu might strike in 2043, but rather to gauge potential trends in the collective frequency, strength and location of hurricanes and other weather features. These findings, in turn, can help inform policy at the state and local levels.

“Such projections can be made in increased confidence by studying the transition of the climate state and engaging people with a local-scale understanding of weather systems,” said climate scientist Kerry Cook of the University of Texas at Austin.

Mann foresees “high-resolution coupled climate models that are more capable of capturing extreme weather events by better capturing the subtle role of climate change on jet stream dynamics and planetary waves, and by better resolving tropical cyclogenesis [cyclone formation] and hurricane behavior.” His own work has pointed to the potential for increasing “stuckness” of extreme summer weather patterns.

Greenhouse emissions in the 2020s

For all its horrific consequences, Covid-19 has nudged humanity’s foot off the fossil-fuel accelerator, if only slightly. Mainly as a result of the pandemic-induced drop-off in transportation and manufacturing, global emissions of human-produced greenhouse gases dropped by an estimated 8.8 percent in the first half of 2020 compared to the same period in 2019, according to one calculation. This was by far the biggest one-year drop in total emissions on record, and roughly double the largest January-to-June drop, which occurred in World War II.

With Covid-related disruption expected to persist both nationally and globally past Inauguration Day, we’re likely to see at least some level of emissions reduction extend well into 2021.

Eventually, as the global economy bounces back, people and institutions will return to long-postponed decisions on everything from new cars to power plants. It remains to be seen how broadly certain adaptations to Covid-19, such as remote work, will persist into the post-pandemic world. Based on all of these actions – and on policies set in the United States and other nations – it’s quite possible that carbon dioxide emissions from fossil fuels have already passed their long-term peak, according to climate scientist Zeke Hasufather of the Breakthrough Institute. Carbon Brief reports that BP is implicitly projecting that peak oil demand is now behind us.

Descending quickly from an emissions peak is exactly what experts say is desperately needed in order to keep the worst climate-change scenarios at bay. A widely publicized 2018 report from the Intergovernmental Panel on Climate Change (IPCC) found that emissions of carbon dioxide need to plummet by around 60 percent between 2018 and 2030 in order for the world to have a two-thirds chance of keeping global temperatures from warming more than 1.5 degrees C above preindustrial values. Beyond 1.5 C, the risk of dangerous tipping points would rise sharply.

Global temperature isn’t far from that 1.5 C threshold right now. A surge of atmospheric warming that brought three consecutive record global highs from 2014 to 2016 has weakened only slightly. Even though 2020 has been transitioning from weak El Niño into potent La Niña conditions, this year is still likely to be the warmest globally in more than a century of record keeping, according to an analysis published in October by Carbon Brief. (Record global highs are more likely during El Niño years, when the eastern tropical Pacific warms and sends heat into the air, and less likely during La Niña years, when the same region is cooler.)

Beyond this year, it will probably take until 2022, and perhaps even longer, for the next global high to be reached. That’s because most of the cooling impact of the current La Niña event will hit during 2021. What’s more, unlike El Niño, La Niña often stretches into episodes that last two or even three years.

Thresholds and impacts

It’s wise not to let the vicissitudes of El Niño and La Niña – natural features of global climate – distract us from the longer-term picture. In its most recent decadal forecast of global temperature, published in January, the U.K. Met Office predicted a slight chance that global temperatures may cross the 1.5 C threshold at some point between now and 2025. If it happens then, this first breach would almost certainly be short-lived; it would take years more for global temperature to remain more consistently at or above 1.5 C, the situation warned about by the IPCC report. Absent major emission reductions, this is simply a matter of time.

The only globe-spanning agreement to date on cutting greenhouse emissions is the Paris Agreement, finalized in late 2015. The accord relies on voluntary pledges from each participating nation, to be updated every five years. In 2017, Trump announced his intent to pull the U.S. out of the agreement – but in a case of quirky timing, the pullout doesn’t become effective under U.N. rules until Nov. 4, the day after the U.S. election. If Biden wins, the U.S. could rejoin the agreement in short order, which he has pledged to do.

The IPCC will soon release its next full climate assessment, the sixth to be produced since 1990 and the first one in almost a decade. The three main components – focusing on physical science, mitigation, and adaptation – are scheduled for release in 2021, with the synthesis report to follow in 2022.

“I think that the most important research of the future is on the impacts side – how climate change will impact humans and how humans can respond,” said climate scientist Andrew Dessler of Texas A&M University. “I also think that research on energy systems will be very important, as will research on how we can remove carbon from the atmosphere.”

Shifts in energy use this decade, such as the ongoing global move away from coal, could have a profound effect on the course of climate change later in the century. Motivated in part by the IPCC’s special report in 2018, a wave of recent studies has focused on comparing and contrasting the climate impacts from 1.5 C versus 2.0 C of warming above preindustrial values. Such work, quantifying the impacts set into motion at various temperature thresholds, has been at the center of Hayhoe’s research for almost two decades. She’s encouraging peers involved with the next U.S. National Climate Assessment, scheduled for 2022, to take this approach.

“We – people, citizens, decision-makers, stakeholders, not just scientists – need to know how each additional half or full degree we warm carries additional impacts, and that the more warming we see, the more likely it is that our systems will fail,” Hayhoe said.

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Bob Henson, a meteorologist and science writer based in Colorado, is the author of “The Thinking Person’s Guide to Climate Change” (AMS Books).

Image credit: Eddiem360, CC-BY-SA-4.0 via Wikimedia Commons