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18291 |
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Date: November 06, 2022 at 10:51:56
From: ryan, [DNS_Address]
Subject: How do we know humans triggered warming? |
URL: https://www.sfgate.com/news/article/Climate-Questions-How-do-we-know-humans-17529832.php |
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Climate Questions: How do we know humans triggered warming?
SETH BORENSTEIN, AP Science Writer
Oct. 24, 2022
Call it Law and Order: Climate Change. Scientists used detective work to pinpoint the prime suspect in Earth’s warming: us.
They proved it couldn’t be anything but carbon dioxide and other greenhouse gases from the burning of fossil fuels.
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EDITOR’S NOTE: This story is part of an ongoing series answering some of the most fundamental questions around climate change, the science behind it, the effects of a warming planet and how the world is addressing it.
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For more than 30 years top scientists from across the globe have worked together every several years to draft a report on climate change and what causes it and with each report — and increases in global temperatures — they have become more and more certain that climate change is caused by human activities. In the latest version of their report they said: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”
Scientists — including the late Ralph Cicerone, the former president of the National Academy of Scientists — have told The Associated Press their confidence in climate change being a human caused problem is equivalent to their certainty in understanding that cigarettes are deadly.
One way to show humans caused the warming “is by eliminating everything else,” said Princeton University climate scientist Gabe Vecchi.
Scientists can calculate how much heat different suspects trap, using a complex understanding of chemistry and physics and feeding that into computer simulations that have been generally accurate in portraying climate, past and future. They measure what they call radiative forcing in watts per meter squared.
The first and most frequent natural suspect is the sun. The sun is what warms Earth in general providing about 1,361 watts per meter squared of heat, year in year out. That’s the baseline, the delicate balance that makes Earth livable. Changes in energy coming from the sun have been minimal, about one-tenth of a watt per meter squared, scientists calculate.
But carbon dioxide from the burning of fossil fuels is now trapping heat to the level of 2.07 watts per meter squared, more than 20 times that of the changes in the sun, according to the U.S. Environmental Protection Agency. Methane, another powerful heat-trapping gas, is at 0.5 watts per meter square.
The sun’s 11-year cycle goes through regular but small ups and downs, but that doesn’t seem to change Earth’s temperature. And if anything the ever so slight changes in 11-year-average solar irradiance have been shifting downward, according to NASA calculations, with the space agency concluding “it is therefore extremely unlikely that the Sun has caused the observed global temperature warming trend over the past century.”
In other words, the sun had an alibi.
The other natural suspects — volcanoes and cosmic rays — had even less influence during the last 150 years of warming, scientists conclude.
The other way to show that it is carbon dioxide causing warming is by building what Vecchi calls “a causal chain.”
National Oceanic and Atmospheric Administration records measured on a Hawaiian volcano show rising carbon dioxide levels as do ice records that go back thousands of years. But the key is what type of carbon dioxide.
There are three types of carbon-containing material. Some contain light carbon, or carbon-12. Some contain heavy carbon or carbon-13 and still others contain radioactive carbon-14.
Over the last century or so, there’s more carbon-12 in the atmosphere compared to carbon-13 and less carbon-14 in recent decades, according to NOAA. Carbon-12 is essentially fossil carbon from long ago, as in fossil fuels. So the change in the ratio of carbon-12 to carbon-13 tells scientists the carbon in the air is more from burning fossil fuels than natural carbon, Vecchi said.
That’s the fingerprint of burning coal, oil and natural gas.
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[18301] [18302] [18292] [18293] [18295] [18296] |
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18301 |
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Date: November 20, 2022 at 18:28:59
From: eaamon, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
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it's too bad none of them are math majors.
they would have figured out that 4 billion in 1977 led to 8 billion in 2007.
but the politicians don't want you to know.
it is going to lead to 16 billion by 2037, my estimate.
look at the numbers yourself and see how fast it is escalating.
add into that China did away with the one child per family and the US did away with abortion.
here in TN there are 1800 kids sleeping in Department of Child Care services as they can not find homes for them now!
since I moved here ten years ago the population here has doubled and the neighboring town has grown by 150% and still adding 400 new homes in the next 6 months.
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[18302] |
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18302 |
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Date: November 20, 2022 at 22:17:53
From: ryan, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
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staggering numbers for sure...nature demands her cut, no matter how pathetic the individual contributions are...
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18292 |
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Date: November 06, 2022 at 10:54:42
From: ryan, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
URL: https://www.sfgate.com/news/article/Climate-Questions-How-does-carbon-dioxide-trap-17524408.php |
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Climate Questions: How does carbon dioxide trap heat?
SETH BORENSTEIN, AP Science Writer
Oct. 21, 2022
That carbon dioxide and other greenhouse gases trap heat is something scientists have known about for more than a 150 years. The underlying concept behind climate change is simple enough that school children can replicate the chemistry and physics and so can you.
The why and how it happens is only a bit more complicated.
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EDITOR’S NOTE: This story is part of an ongoing series answering some of the most fundamental questions around climate change, the science behind it, the effects of a warming planet and how the world is addressing it.
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Just as a greenhouse traps heat or a blanket keeps you warm, carbon dioxide, methane and other gases — nicknamed greenhouse gases — trap heat from the sun that would otherwise bounce back into space. The blanket or greenhouse aren’t perfect analogies but they give the right sense of what is happening, said University of Pennsylvania climate scientist Michael Mann.
Without the greenhouse effect, Earth would be freezing, scientists said. The greenhouse effect, which is natural but then put on steroids by carbon pollution, is responsible for conditions that make life on Earth possible.
But there can be too much of a good thing. Scientists point to the runaway greenhouse effect on Venus as a case example. In fact, former top NASA climate scientist James Hansen, often called the Godfather of global warming, initially was studying what was happening on Venus before he turned to his home planet and accurately warned people about a smaller scale version happening here.
Heat from the sun comes through the atmosphere and then bounces back as infrared radiation, a different wavelength than it came in on. If you put your hand over a dark rock on a warm sunny day you may be able to feel that heat heading off Earth. The greenhouse effect is when that heat tries to escape Earth, but some of it is trapped by different chemicals in the atmosphere, such as water vapor, carbon dioxide and methane.
In the 1820s, French mathematician and scientist Joseph Fourier figured that something keeps Earth warmer than a bare rock out in space: Our atmosphere.
“Our atmosphere, thrown as a barrier across the terrestrial rays, produces a local heightening of the temperature at the Earth’s surface,” Irish physicist John Tyndall said in 1862, identifying water vapor and carbon dioxide as natural greenhouse gases trapping heat. Then in 1896, Swedish chemist Svante Arrhenius took it one step further and calculated that changes in carbon dioxide may affect the climate.
Many classroom and even home kitchen experiments can show this with two plastic soda bottles, some carbon dioxide, air, a strong light bulb or flame and a thermometer. Heat up a bottle with regular air and one filled with carbon dioxide in similar ways, take their temperatures and after a while the carbon dioxide filled one should warm noticeably more.
That’s because of the geometry, spin and vibration of carbon molecules block the specific infrared wavelength of light that’s trying to escape Earth, Mann said. It’s a different wavelength than the light heading into the sun.
Greenhouse gases, especially carbon dioxide, “correspond to sort of holes” in the light spectrum that would otherwise allow heat to escape, but they block the exits, Mann said.
But if there are natural greenhouse gases why do small changes in carbon dioxide levels matter?
Earth’s carbon dioxide levels are about 420 parts per million, compared to 280 before the industrial revolution and the Earth has warmed about 2 degrees (1.1 degrees Celsius) in that time. Mann suggests another home experiment. Take a clear bowl of water. Put a few drops, say 0.4% of the water, of black ink in it.
“And the water turns black now,” Mann said. “Certain chemicals can have a very potent impact in very low concentrations. It’s true of cyanide. That’s why we avoid cyanide in even lower concentrations than that. And the ink experiment really drives how much of an influence a small number of very potent molecules can have... And that’s what’s going on here.”
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[18293] [18295] [18296] |
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18293 |
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Date: November 07, 2022 at 16:49:36
From: Sue/Seattle, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
URL: https://www.britannica.com/explore/savingearth/climate-change-throughout-history |
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Really good and long article on climate change linked.
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[18295] [18296] |
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18295 |
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Date: November 08, 2022 at 12:16:57
From: akira, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
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thanks, that was fascinating & really important info. Merely focusing on the
past 150 years without including this perspective is pointless.
the last paragraph:
"Humans and other species have survived countless climatic changes in the
past, and humans are a notably adaptable species. Adjustment to climatic
changes, whether it is biological (as in the case of other species) or cultural
(for humans), is easiest and least catastrophic when the changes are gradual
and can be anticipated to large extent. Rapid changes are more difficult to
adapt to and incur more disruption and risk. Abrupt changes, especially
unanticipated climate surprises, put human cultures and societies, as well as
both the populations of other species and the ecosystems they inhabit, at
considerable risk of severe disruption. Such changes may well be within
humanity’s capacity to adapt, but not without paying severe penalties in the
form of economic, ecological, agricultural, human health, and other
disruptions. Knowledge of past climate variability provides guidelines on the
natural variability and sensitivity of the Earth system. This knowledge also
helps identify the risks associated with altering the Earth system with
greenhouse gas emissions and regional to global-scale changes in land
cover."
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[18296] |
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18296 |
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Date: November 08, 2022 at 19:54:21
From: ao, [DNS_Address]
Subject: Re: How do we know humans triggered warming? |
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I think our adaptability to changes is a variable that, in large measure, is equal to our ability to peacefully coexist.
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