"The suggestion that natural causes are contributing to global warming is entirely speculative. If someone proposes that natural causes are warming the earth, they need to identify, observe and quantify the specific process that is occurring. It may be true that unicorn farts, rather than greenhouse gases, are warming the earth over the past century. But the burden of proof is on the unicorn advocates. They need to find the unicorns, observe and measure the heat generated per unicorn fart. They need to demonstrate that unicorn farts are sufficient to account for a significant portion of global warming, and to either discredit the physics of greenhouse gases or to identify a previously undetected heat sink on the scale of the global ocean to account for the displacement of greenhouse gas heat. They also need to demonstrate that unicorn farts are delivering heat to the surface of the ocean and cooling the stratosphere. The notion that “we just don’t know what is warming the earth” is not a viable statement.
I recently had a call with a staffer for Alaska’s more conservative U.S. Senator. I had made a trip to DC, and Alaska’s Congressional Delegation will usually make time to meet with constituents who travel 3350 miles from home. I had sent meeting requests to both Senators, and the moderate Senator’s staff contacted me, and we had a good discussion of climate change. The more conservative Senator’s office contacted me after I sent a complaint comparing their non-responsiveness to the moderate Senator. In my call with the staffer, I discussed the points on my agenda:
1) That we needed to cut CO2 emissions 50% by the year 2035 and to zero by 2050, to avoid a climate disaster.
2) Achieving those cuts will be very difficult and costly. Real climate solutions need to be affordable, scalable, timely, environmentally acceptable, and technologically mature. There are no currently viable solutions, as global upscaling of renewable energy runs into problems with increasing costs and timeliness.
3) We cannot count on negative emissions technologies to provide a climate solution due to similar issues with global scaling of these technologies.
4) Historically, the United States disproportionally contributed to the climate crisis, and we will be held responsible, accountable, and liable for damages to other nations in the future.
5) Because we are disproportionally to blame, we are morally obligated to lead the world in reducing emissions.
6) In the case of south-central Alaska, replacing our fossil-fuel electrical generation will require about 1000 new wind turbines, plus short-term and seasonal energy storage. Powering a full fleet of electric vehicles will require at least another 1000 wind turbines, and replacing space heating by fossil fuels will require at least another 1000 wind turbines, all to be accomplished by 2050. For reference, building an 11-turbine wind farm near Anchorage required a decade of planning and two years of construction.
7) A carbon tax is the best way to meet emission reduction goals, starting small, and increasing until renewable energy or carbon sequestration is commercially justified.
The staffer listened politely to my sermon, at points offering small interjections. He commented that the Senator sponsored legislation to reduce the permitting obstacles to building more wind turbines. I responded that it was a nice ideological gesture, but the real problem in building more wind energy wasn’t permitting, it was the availability of capital. The great majority of cost for fossil-fuel generation is in fuel expense, which is spread out across the life of the power plant. The great majority of cost for renewable energy is in capital, which must be funded up-front. The staffer added that it was an exciting time for renewable energy; and that there was much interest and activity in Congress for doing more.
At the end of our conversation, I took issue with one of the Senator’s canned response letters regarding climate change. The Senator’s previous position was that we don’t know how much of climate change is due to human greenhouse gas emissions, and how much is due to natural factors. I said that was false. “It is?” questioned the staffer, sounding surprised. “Yes”, I replied. “That’s complete bullshit. All of climate change is due to human influences; one hundred percent. There are no natural processes or cycles that are adding heat to the earth to the degree and over the time frame that we have observed global warming.” Shortly afterward, we concluded the call.
In retrospect, I wasted a good opportunity to provide a real explanation to someone who could make a difference in forming policy. In the fashion of introverts everywhere, here is what I should have said.
Global warming is by now a well-quantified problem. The physics of greenhouse gases has been understood for 125 years. The physics of global warming has been well-quantified since the 1980s, when satellites began measuring incoming solar radiation, and outgoing radiation was measured at the surface, and at various altitudes up to the stratosphere, and later by satellites. What was happening to that heat was still somewhat uncertain in the 1990s, but in the early 2000s instrumentation was devised to measure the temperature of the ocean to a depth of 2000 meters, and to monitor the mass of the polar ice caps, Arctic sea ice, and continental glaciers. The system of measuring surface temperatures was also improved with the addition of satellite observations. Considering all of this information, we now have twenty years of comprehensive measurements for the earth’s heat budget.
The first point is that heat from greenhouse gases is fully sufficient to account for the heat now appearing in earth’s heat sinks, with an imbalance of only a few percent. If a natural source of heating existed, it would raise another problem – what is happening to the heat from greenhouse gases? In order to validate a natural source of heat, either the physics of greenhouse gases needs to be overturned (which isn’t going to happen), or we have somehow overlooked a heat sink on the scale of the global ocean. This also is extremely unlikely.
A second point is that any alternative explanation of global warming must also explain the pattern of heat flow. Observations show that the oceans, which absorb more than 90% of the heat from greenhouse gases, are warming from the surface downwards. This implies heating at the surface, either from increased solar radiation or by conduction from the atmosphere. We have forty years of satellite observations of the solar radiation, conclusively proving that the solar radiation is declining slightly, not increasing. Any speculative natural process for global warming must necessarily deliver heat to the surface of the ocean, from the atmosphere. This rules out any speculative heat source involving ocean currents or cycles.
A final point is that there are no known natural systems adding new heat to the earth over the past five decades. Geologists, oceanographers, and meteorologists have done a pretty good job over the past 200 years, identifying the processes operating on the earth's surface. No process that would add new heat to the planet's surface, over the time that global warming has occurred, has been identified. Natural systems do have some cyclicity that affect the global climate. Ocean cycles generally operate over periods of a decade or less, not over the multi-decade time scale that we observe heat appearing in earth systems. But one important thing to note is that these natural cycles are zero-sum; they redistribute heat but don’t add new heat to the earth. As noted above, solar radiation varies according to the eleven-year solar cycle, but there is no continuing warming persisting beyond those cycles.
The argument that natural causes are contributing to climate change is entirely speculative. If someone is proposing that natural causes are warming the earth, they need to identify, observe and quantify the specific process that is occurring. It may be true that unicorn farts are warming the earth, rather than greenhouse gases. But the burden of proof is on the unicorn advocates, to find the unicorns, observe and measure the heat generated per unicorn fart. They need to demonstrate that unicorn farts are sufficient to account for a significant portion of global warming, and to either discredit the physics of greenhouse gases or to identify a previously undetected heat sink on the scale of the global ocean, to account for the displacement of greenhouse gas heat. They also need to demonstrate that unicorn farts are delivering heat to the surface of the ocean, and cooling the stratosphere.
The notion that “we just don’t know what is warming the earth” is not a viable statement.
Written testimony of climatologist Zeke Hausfather to the US House Committee on Space, Science and Technology, , p. 13, 3/12/2021 https://science.house.gov/imo/media/doc/Hausfather%20Testimony.pdf
“Our best estimate is that approximately all of the observed global mean surface temperature warming since the 1950s is due to human emissions of CO2 and other greenhouse gases. Natural climate “forcings” such as changing solar output, variations in the Earth’s orbit, and volcanic activity would have likely led to a slight cooling over the past 70 years in the absence of human influences on the climate.”
IPCC 6th Assessment Report, Headline Statements from the Summary for Policymakers, 8/9/2021 (draft) https://www.ipcc.ch/report/ar6/wg1/#SPM
“A.1 It is unequivocal that human influence has warmed the atmosphere, ocean and land.” – Policy-makers’ Headline Statements, first line.
“Human influence on the climate system is now an established fact:…It is unequivocal that the increase of CO2, methane (CH4) and nitrous oxide (N2O) in the atmosphere over the industrial era is the result of human activities and that human influence is the principal driver of many changes observed across the atmosphere, ocean, cryosphere and biosphere.” Pg. TS-8
“Table TS.1: Synthesis: Warming of the global climate system since preindustrial times], Observed Change Assessment – Established Fact; Human Contribution Assessment – Established Fact.” Pg. TS-33.
‘Less than 1% probability’ that Earth’s energy imbalance increase occurred naturally, say Princeton and GFDL scientists, Liz Fuller-Wright, 2021. https://www.princeton.edu/news/2021/07/28/less-1-probability-earths-energy-imbalance-increase-occurred-naturally-say
“[Shiv Priyam Raghuraman] and his co-authors used satellite observations from 2001 to 2020 and found that Earth’s “energy imbalance” is growing….’It is exceptionally unlikely — less than 1% probability — that this trend can be explained by natural variations in the climate system,’ said Raghuraman.”
Anthropogenic forcing and response yield observed positive trend in Earth’s energy imbalance, Reghuraman et al, 2021. https://www.nature.com/articles/s41467-021-24544-4