The scientific debate is over: it is time to act on climate change

Credit: IPCC

The facts of climate change

At this point in time, the basic facts of climate change are not disputable in the least. Careful planet-wide observations by NASA and others have confirmed that 2018 was the fourth-warmest year in recorded history. The only warmer years were 2016, 2017 and 2015, respectively, and 18 of the 19 warmest years in history have occurred since 2001. Countless observational studies and supercomputer simulations have confirmed both the fact of warming and the conclusion that this warming is principally due to human activity. These studies and computations have been scrutinized in great detail by a climate science community numbering in the thousands, representing all major nations, as summarized in the latest report by the Intergovernmental Panel on Climate Change (IPCC).

Debunking climate change myths

Climate change skeptics continue to raise objections, claiming that there is “scientific evidence” that this mainstream consensus on climate change is wrong. But these objections have been debunked many times. Here are some examples:

  1. Climate change is just part of the natural cycle. Rejoinder: Yes, the geologic and paleontological record confirms numerous climate changes in the past. But the changes of the past 150 years, coinciding with the industrial revolution and huge increases in carbon emissions, exceeds that of the past five million years. See also this Scientific American article.
  2. Changes are due to sunspots or galactic cosmic rays. Rejoinder: Scientists who have carefully monitored the sun for at least the past 20 years have seen no significant upward trend. Besides, such effects would be seen in the high atmosphere, whereas observed climate change effects are seen in the lower atmosphere. See also this Carbon Brief article.
  3. CO2 is a small part of the atmosphere, so it can’t have a large heating effect. Rejoinder: The fact that CO2 results in a greenhouse warming effect has been known since 1856, and countless experimental analyses since then have confirmed heating even with only very small concentrations.
  4. Scientists manipulate datasets to show a warming trend. Rejoinder: Yes, scientists adjust data, as in all experimental studies, but these adjustments are performed based on very well-understood effects, and are open to the scrutiny of peers.
  5. Climate models are unreliable and too sensitive to carbon dioxide. Rejoinder Climate models are extremely sophisticated computer programs, running on some of the world’s most powerful supercomputers, and based on massive experimental datasets. These models have been produced by numerous independent international teams, which rigorously critique each other’s work, in an ongoing process of peer review. All of the latest models consistently now predict significant long-term global warming. See for example the Community Earth System Model website.

A climate skeptic changed his mind

Along this line, it is worth pointing out that some previous climate skeptics have changed their mind. For example, in a remarkable New York Times Op-Ed, former climate change skeptic Richard Muller of the University of California, Berkeley, declared not only that global warming is real, but also that “humans are almost entirely the cause.”

Muller’s Berkeley Earth group approached the problem by rigorously analyzing historic temperature reports. As he described their efforts,

We carefully studied issues raised by skeptics: biases from urban heating (we duplicated our results using rural data alone), from data selection (prior groups selected fewer than 20 percent of the available temperature stations; we used virtually 100 percent), from poor station quality (we separately analyzed good stations and poor ones) and from human intervention and data adjustment (our work is completely automated and hands-off). In our papers we demonstrate that none of these potentially troublesome effects unduly biased our conclusions.

Muller noted that their record of temperatures is long enough that they could search for the fingerprint of variability in the sun’s output reaching the earth. But Muller found no such fingerprint. Global warming is real.

So how much, if any, of this warming can truly be ascribed to human activity? Muller’s Berkeley Earth group found that the record of temperatures over the past 250 years fits the increasing emissions of CO2 better than any other statistic they tried, and the magnitude of the change is entirely consistent with the known greenhouse effect of CO2.

Scientific consensus versus public views on climate

At this point in time, at least 97% of climate science researchers agree with the central conclusion that the Earth is warming and that human activity is the primary cause. This statistic is based on multiple in-depth surveys of thousands of recently published papers in the climate science field. Further, this consensus is supported by official statements from the American Association for the Advancement of Science, the American Chemical Society, the American Geophysical Union, the American Meteorological Society, the American Physical Society, the Geological Society of America, the U.S. National Academy of Sciences and numerous other scientific societies worldwide.

In contrast, large numbers of Americans in particular continue to deny even the most basic facts. In a 2017 Pew Research Center survey, 23% denied that there is any solid evidence that the Earth has been warming, and of those who acknowledge warming, nearly half doubted that it is due to human activities.

So why are so many skeptical of the scientific consensus? According to a separate 2017 Pew Research Center survey, only 27% agreed that “almost all” scientists are in agreement; 35% said only “More than half,” and 35% said half or fewer. But even more disturbingly, only 32% agreed that the “best available scientific evidence” influences the climate scientists’ conclusions; 48% said only “some of the time”, and 18% said “not too often or never.” These results underscore a severe level of distrust of scientists in general and climate scientists in particular by the public.

Climate change is already having a major impact

According to the latest IPCC report, impacts on natural and human systems are already occurring, and even a warming of 1.5 C, which at this point can hardly be averted, will have very serious consequences, including more extreme temperature events, more instances of heavy precipitation, more severe droughts, rising sea levels damaging cities and agricultural lands, as well as enormous stress on ecosystems worldwide.

An October 2019 Scientific American article listed some of the frightening developments, just in the previous 12 months:

  1. In December 2018, the World Health Organization said that fossil fuel emissions are “a major contributor to health-damaging air pollution, which every year kills over seven million people.” It added that extreme weather events, which have been linked to human-caused climate change, are “a clear and present danger to health security.”
  2. Also in December 2018, the Global Carbon Project reported that global CO2 emissions reached an all-time high in 2018, up more than two percent after three level years. What’s more, additional increases are likely in 2019.
  3. In April 2019, a NASA-funded study found the mass loss of ice discharged into the ocean from Greenland glaciers had increased by a factor of six since the 1980s. Partly as a result, mean sea level has risen nearly 14 millimeters since 1972, with 7 millimeters in the past eight years. Subsequently, in July 2019, a severe Arctic heat wave resulted in 12.5 billion tons of ice melting into the ocean on a single day, the largest single-day loss on record.
  4. In May 2019, a United Nations biodiversity panel reported that over one million animal and plant species are threatened with extinction in the next few decades, and, further, that rates of extinction are “accelerating.”
  5. In September 2019, an IPCC report concluded that warming oceans, melting ice, and rising sea levels are already affecting 10 percent of the world’s population that lives in low-lying coastal areas, and that negative impacts will greatly worsen in the coming years and decades.
  6. In October 2019, California staggered through its third consecutive catastrophic wildfire season, with thousands of fires incinerating tens of thousands of acres, and, once again, causing billions of dollars in damages. This is in spite of the unprecedented step of pre-emptively shutting off power to large portions of the state in an effort to prevent downed power lines from generating more fires, a step that in effect reduced the world’s premier high technology leader and fifth largest economy to third-world status. The consensus of scientists is that the dry autumn weather and winds that precipitated these fires are exacerbated by climate change, with the dismal prospect for even more wildfires and power blackouts in the future.

“How dare you?”

So where do we go from here? Sixteen-year-old Swedish activist Greta Thunberg said it best in her eloquent remarks to the 2019 U.N. Climate Summit (excerpt):

You have stolen my dreams and my childhood with your empty words. And yet I’m one of the lucky ones. People are suffering. People are dying. Entire ecosystems are collapsing. We are in the beginning of a mass extinction, and all you can talk about is money and fairy tales of eternal economic growth. How dare you!

For more than 30 years, the science has been crystal clear. How dare you continue to look away and come here saying that you’re doing enough, when the politics and solutions needed are still nowhere in sight.

You say you hear us and that you understand the urgency. But no matter how sad and angry I am, I do not want to believe that. Because if you really understood the situation and still kept on failing to act, then you would be evil. And that I refuse to believe.

The popular idea of cutting our emissions in half in 10 years only gives us a 50% chance of staying below 1.5 degrees [Celsius], and the risk of setting off irreversible chain reactions beyond human control.

Fifty percent may be acceptable to you. But those numbers do not include tipping points, most feedback loops, additional warming hidden by toxic air pollution or the aspects of equity and climate justice. They also rely on my generation sucking hundreds of billions of tons of your CO2 out of the air with technologies that barely exist.

So a 50% risk is simply not acceptable to us — we who have to live with the consequences.

To have a 67% chance of staying below a 1.5 degrees global temperature rise – the best odds given by the [Intergovernmental Panel on Climate Change] – the world had 420 gigatons of CO2 left to emit back on Jan. 1st, 2018. Today that figure is already down to less than 350 gigatons.

How dare you pretend that this can be solved with just ‘business as usual’ and some technical solutions? With today’s emissions levels, that remaining CO2 budget will be entirely gone within less than 8 1/2 years.

There will not be any solutions or plans presented in line with these figures here today, because these numbers are too uncomfortable. And you are still not mature enough to tell it like it is.

You are failing us. But the young people are starting to understand your betrayal. The eyes of all future generations are upon you. And if you choose to fail us, I say: We will never forgive you.

We will not let you get away with this. Right here, right now is where we draw the line. The world is waking up. And change is coming, whether you like it or not.

[This originally appeared in the Math Scholar blog.]

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