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OPINION | ART HOBSON: Blockbuster UN report details looming threat from global warming – Northwest Arkansas Democrat-Gazette

As wildfires consume northwestern forests, hurricanes batter our coast, rising seas threaten Miami, drought bakes California, extreme rain destroys Tennessee cities and extreme heat hits Seattle, Americans are finally awakening to the reality of global warming.

It’s been a long time coming. I began teaching the topic in general physics courses around 1975, and railed about it in these pages beginning with my first op-ed piece in 2002. Many scientists began sounding alarms when the evidence became persuasive during the 1970s, oil companies knew global warming was a threat and yet denied it during the 1980s, and the first United Nations report on global warming appeared in 1990.

Now the Scientific Assessment portion of the sixth U.N. report has appeared. It’s a 3,000-page, 234-author scientific masterpiece and a social blockbuster. It’s the first part of a broader three-part report; Part Two will discuss policies to reduce global warming emissions, while Part Three will present adaptive responses to warming.

According to the report, it’s “established fact” that human activities are causing Earth to warm, that greenhouse gas levels are now the highest in over 2 million years, and that climate change’s impact on the planet is “unprecedented.” This blunt language reflects the remarkable scientific advances since the fifth U.N. assessment in 2013.

The report is freely available on the web, including at https://www.ipcc.ch/report/ar6/wg1/ . It’s filled with fascinating details and written in non-technical language. Here’s one example of these details: In order to portray our understanding of hot extremes (“heat waves”) such as the temperatures of 108 to 116 degrees Fahrenheit that occurred in Portland, Seattle and British Columbia during several days in late June, Earth’s inhabited area is broken down into 45 contiguous regions. Each region is rated as to whether the annual number of hot extremes has significantly increased (which it did in 41 regions), decreased (zero regions), or neither (4 regions), and also as to our scientific confidence that the observed change is due to human causes (high confidence in 24 regions, medium confidence in 15 regions, low confidence in six regions).

Five increasingly dire possible scenarios for Earth’s climate future present the report’s most crucial message. These scenarios should be compared with the recommendation from the 2015 Paris Climate Conference, namely that we must limit global average temperatures to less than 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial temperatures. The problem is, we’ve already raised temperatures by 1.1 of those allowable 2 degrees and we’re now seeing the disastrous results. The scenarios investigate what happens in a world whose temperature rise (or “warming”) reaches a maximum 1.5 degrees, 2 degrees, 4 degrees, 5 degrees and 7 degrees.

As a typical example of the difference between scenarios, consider an extreme heating event that (on average) would occur only once in 50 years if we lived in a pre-industrial climate. The 1.5-degree scenario implies this event occurs 5 times in 50 years, while the 4-degree scenario implies it occurs 39 times in 50 years. The message is that very rare events become common in a warmer world.

Unfortunately, we already have essentially zero chance to stay within a 1.5-degree limit. In the best imaginable case, annual emissions drop to zero by 2050 and warming is limited to 1.6 degrees. But today we are not even remotely on a path to achieve this: Emissions are far above zero. Far from decreasing, annual emissions are in fact increasing. Our carbon-energized economy is pushing global emissions higher every year and we will exceed the 1.5-degree limit by 2030.

To limit warming to 2 degrees, we’ve got to turn increasing annual emissions around, and then decrease emissions all the way to net zero by 2050 (“net” zero because small emission levels could be balanced by carbon-consuming technological devices). This is still possible, but implausible given our fossil-fuel-guzzling habits.

So unless we rapidly change our ways, we’re on one of the three higher-temperature paths. These scenarios range from terrible to ghastly. It seems to me that the continuing environmental havoc could spell the end of democracy everywhere. These scenarios imply massive Antarctic ice sheet loss, a possibility of Antarctic ice sheet failure, more extreme and far more frequent heat waves, more extreme and more frequent rainfall, four times more drought, a nearly ice-free summertime Arctic Ocean by 2050, catastrophic sea-level rise and a far more acidic ocean.

The 26th U.N. Climate Change Conference, a successor of the 2015 Paris Conference, will happen in Glascow, Scotland, from Nov. 1-12. This could be a do-or-die moment for civilization. Please pay attention.

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