Is climate change real? How to decide for yourself.
Updated: Oct 15, 2021
How do you figure out the truth of any topic these days, much less one as deep and technical as climate change? I read many points of view from people more expert than I and felt I would never really be able to get to the bottom of the question.
But I discovered how to separate the central question from the noise. I went back to the official sources. Without devoting weeks to research, I figured out what climate scientists actually do, what they're saying, and why they're saying it.
I reached the clarity I was looking for, and you can too. Here's how.
Focus on the core claim
Climate can mean a million things, from coral beds to forest fires to hurricanes. Change might mean more hurricanes, or fewer, or bigger ones, or longer-lasting ones, or starting earlier in the season, or traveling faster, or hitting land more often. Whatever bit of climate you see out your window, you can find a hundred ways it has changed from how it used to be.
Your town may face real problems that come under the broad label of climate. If you live in Jakarta, sea level rise is an urgent threat. Not because polar ice caps are melting, but because decades of groundwater pumping sink the city a half inch every month. Conditions around us do change, sometimes in adverse ways that need remediation.
But the "climate change" of global politics isn't an idle marvel upon the endless ways the ecosystem shifts, it's a specific causal narrative. It claims fossil fuel emissions cause major shifts and unless we curtail their use will cause significantly worse ones in the future.
That narrative rests on a core scientific claim about the greenhouse effect. Visible sunlight warms the earth, making it glow slightly in the infrared. That glow radiates energy back into space. By conservation of energy, the earth will warm to the point the infrared radiation going out balances the sun's energy coming in.
Carbon dioxide, methane and other greenhouse gases shift the energy balance. They're transparent to sunlight coming in but they absorb infrared trying to escape. The more CO2 we have in the atmosphere, the more escaping heat gets trapped. The earth warms and therefore glows brighter, until the energy that makes it into space is once again in balance with energy coming in from the sun.
The dots to be connected
No one disputes that CO2 levels are rising. And no one disputes that higher CO2 levels mean a warmer planet, all other things being equal. It's not clear how strong the temperature response is, since the atmosphere is already fairly opaque in the specific bands CO2 absorbs. Adding more might be like the fifth coat of red paint on the barn--it can't get much redder than it already is.
And other things will certainly not stay equal. Higher temperatures melt bright ice into dark ocean, absorbing more of the sun's energy and pushing the equilibrium temperature up. On the other hand higher evaporation means more clouds, which reflect sunlight and push the equilibrium temperature down. At least, usually. Snow and ice are brighter than clouds, so clouds over Antarctica make it slightly darker and have the opposite effect. It's not obvious how all these complex processes net out.
Finally it's not obvious which, if any, of the local events people blame on "climate change" has anything to do with long-term trends in the earth's average temperature. We remark on floods and heat waves precisely when they reach extremes that flout the average.
If averages drive extremes, it's not obvious how. People have gotten taller over the past century or so, but no one would consider that a satisfactory explanation of a village of 8-foot humans. If CO2 caused global temperatures to rise 2° over the past 200 years, how did that cause a 20° heat wave in Toronto for a week? A causal linkage between CO2 averages and local climate extremes cannot be taken for granted.
The core question of climate change, then, is not whether blizzards here or wildfires there are getting worse, it's the causal hypotheses that (a) rising CO2 levels cause significant average temperature increases which (b) in turn drive local weather extremes the media reports as signs of climate change.
Read the sources
Having pruned down the question, where do you turn for the answer? Trace the claims back to their source. Individual research teams around the world are investigating specific questions about ice cores or tree rings, but on the big question of CO2's effects on the global climate, the United Nations represents the institutional consensus. The UN formed the Intergovernmental Panel on Climate Change (IPCC) in 1988 which every six years or so publishes a set of Assessment Reports on climate science, impacts, and policy options. If you read even one, odds are you'll be better informed than most journalists and every Extinction Rebellion member.
Climate change is one of those follow-the-science topics, where every politician and activist claims to be deferring to the wisdom of the labcoat class, whether or not they read any of their work. The IPCC purports to represent the consensus of climate researchers around the globe, so to the extent there is an authority distillation of what the science says, this is it.
I certainly can't claim the domain knowledge of the specialists working in this field for decades, and probably neither can you. But we can understand the scientific method. It calls on researchers to conform their conclusions to the data rather than the other way around. The researcher is supposed to put himself out on a limb with a testable hypothesis, which experiment will confirm or dash to pieces. He's supposed to crowdsource QA of his work by publishing his data and inviting others to challenge his conclusions.
Here are some things you should expect to see in a scientifically sound climate report:
Clear predictions about how the climate will behave in the future, given various assumptions about CO2 emissions.
Scorecards of how previous predictions were borne out or refuted by subsequent data during the 26+ years IPCC's researchers have been publishing.
Comparison of the greenhouse climate model to the "null hypothesis" of no special warming--a critical statistical test that penalizes vague predictions. "It might rain tomorrow," for example, is 100% accurate but has no predictive power and would fail this test.
On the other hand, be on the lookout for signs the authors have an agenda other than scientific understanding.
Cryptic qualifying language. "Potential impacts," for example, is conspicuously more speculative than "likely impacts." Is what follows science or science fiction?
Confirmation bias. Beware titles like "Validation of climate models" or "Detection of the greenhouse effect in the observations," which suggest researchers looking for evidence to confirm models. Scientific models can't be confirmed by data, only refuted.
Hiding the report card. The most important question is how well models predict future climate. If these graphs are missing or drawn to obscure the comparison, that is a significant bit of information about the authors.
What you'll find in the IPCC reports
Like its parent UN, the IPCC is a political bureaucracy. Its three working groups create assessment reports, which the IPCC stitches into a synthesis report. There have been five such report cycles since 1990.
Only the first working group speaks for "the science." It predicts what temperatures and other physical metrics might result from various CO2 emission scenarios. The second group riffs on the output of the first, imagining what economic and social impacts might result from climate changes. The third group proposes interventions government policymakers might implement.
What climate scientists do
From reading the first working group's reports, you will learn climate science is all about numerical simulation. The physics of how infrared light interacts with CO2 molecules is a career all by itself, and that's just one of a million dynamics driving the earth's climate. No one can understand them all or account for the interplay between them. The only feasible methodology is to build simplified conceptual models of the atmosphere and sunlight and clouds and oceans and so on, stack them into a hypothetical earth, run numerical simulations and tune it to match climate measurements from the past.
If that sounds like a hedge fund trying to predict the stock market, well, yes it does. Stock
traders develop "systems" for trading, validate them through numerical simulations against historical market prices, and often go broke when future conditions play out differently. A trader who has hit upon a consistently winning system doesn't necessarily understand the market any better than anyone else. And conditions may shift on him next week, putting him suddenly in the red.
As the figure above shows, the climatologists publish the results of many models for each of various emissions scenarios, and there's a significant spread in what the models predict. They're leveraging what the trader would call a portfolio strategy.
Working Group I is focused primarily on predicting temperatures, since that's what the greenhouse effect affects. But each of their models is a virtual earth where SimScotland freezes, the SimNile boils, the growing season in SimUkraine shortens, and whatever else plays out in the computer.
Understanding this methodology is critical for putting climate-related news stories into context. The climate is a chaotic system where everything interacts with everything else and "effects" can't be traced to "causes." A real-world drought leaves no footprints for scientists to follow back to particular temperature fluctuations and particular CO2 levels. When researchers or journalists write a drought in Texas is "linked to climate change", the most scientific justification they might have is that such a drought occurred in some of the SimTexi. Of course with enough simulations, everything happens in SimTexas, from droughts to monsoons to plagues of unicyclists.
If Working Group I are the computer jocks, Working Group II are the sociologists. They take the possibilities generated from the simulations and suggest ways to think about their impact on society. You'll find their reports are mostly conceptual. Their AR5 report mentions justice 62 times, synergy 134. Their graphics are irresistible, if not always actionable.
Working Group III also builds on the emissions scenarios of the scientific working group. It analyzes what parts of the world and what parts of the economy emit greenhouse gases, and hypothesizes trajectories by which governments might act to lower emissions.
How reliable are climate models?
The trillions governments spend on climate policy, including the budgets of the IPCC's scientists and non-scientists, are predicated on the theories that CO2 concentrations drive temperatures, and that increases of a few degrees in global average temperatures cause severe disruptions on a local level. They are also claiming the converse--that if governments act to curtail emissions, the earth's climate will follow a milder course.
The entire edifice rests on Working Group I's ability to predict temperatures and other climate effects for a given emissions scenario. If they can't, we can't be confident that the pain of reducing emissions will pay off in any climate benefit at all. More fundamentally, a CO2 model of climate that gets the climate wrong has no scientific validity.
When AR5--the latest official report--was published in 2014, the IPCC had been in business for 25 years, long enough to evaluate past predictions against subsequent trends. Working Group I assesses model quality in Chapter 9. The money shot appears on page 771.
If you want to judge climate change based on the scientific method, this is the graph to understand. The test of a model's validity is not how many scientists like it but how well it predicts future observations.
This graph looks terrible to me. The IPCC hedges with a big range of predictions and even so overestimates warming by 2x, 5x, and even 10x. Not during a one-month blip but over nearly a decade and a half. As a scientist, throwing these lads out of my office would comport perfectly with the scientific method, since after 25 years of work they can't show better predictive power than astrology.
But read Chapter 9 yourself and see how the IPCC discusses its own results. Draw your own conclusions, because voters around the world have important questions to answer. How much of our resources as taxpayers do we want to funnel to the IPCC and the research teams it represents, to refine climate models and continue policy advocacy? Which CO2 mitigation interventions should governments impose on citizens? What infrastructure projects are we prepared to fund to handle the coming sea level rise and other consequences of CO2 emissions? How sound is the scientific basis for any of those interventions?