The Science of Climate Change: What the Physics Actually Says

The IPCC — the Intergovernmental Panel on Climate Change — is probably the most misrepresented scientific institution in public discourse. Both climate advocates and skeptics tend to mischaracterize what it does and what it says, in opposite directions.

Here's what the IPCC actually is: it's not a research institution that generates new data. It's a review body — a large-scale systematic literature review that synthesizes what the existing peer-reviewed scientific literature says about climate change. The Sixth Assessment Report (AR6), completed between 2021 and 2022, reviewed thousands of studies and involved hundreds of contributing authors. Its conclusions reflect the scientific consensus at the time of publication.

The process has important characteristics. The Summary for Policymakers documents — the parts most widely read and cited — are reviewed and approved by government representatives from member nations, including major fossil fuel producers. This approval-by-consensus process tends to produce language that is more conservative (in the sense of cautious) than the underlying scientific literature, because any government that objects to specific language can hold up the process. Scientists have noted that IPCC projections have historically underestimated observed changes in sea level rise, ice loss, and extreme weather events compared to observations published after the assessment.

What the AR6 actually says, stripped of diplomatic hedging:

Global temperatures have risen 1.1°C above pre-industrial baseline as of the report's cutoff date. This warming is "unequivocally" (their word, stronger than previous reports) caused by human activities, primarily burning fossil fuels.

The scenarios matter enormously. Under the lowest emissions scenario (SSP1-1.9), which requires reaching net zero CO₂ emissions by around 2050 and significant negative emissions after that, peak warming is likely limited to 1.5°C above pre-industrial levels, with a possible temporary overshoot. Under SSP5-8.5 (continuing high emissions growth), warming of 4-5°C by 2100 is within the likely range, with sea level rise of 1-2 meters.

The 1.5°C threshold from the Paris Agreement is significant not because the climate system knows about Paris, but because the science suggests that above 1.5°C, the frequency and severity of extreme weather events, risks to biodiversity, and risks to food systems increase substantially compared to lower warming levels. The 2°C threshold sees these risks increase further. These thresholds are not cliffs — the difference between 1.4°C and 1.6°C is not catastrophic versus fine — they're benchmarks in a continuous risk function.

On current trajectory — implementing all current national policies — we're on track for about 2.7-3°C of warming by 2100 according to Climate Action Tracker. Including all national pledges and targets (which are not policies, just aspirations), the projection is about 1.8-2.4°C. The gap between current policies and stated targets is real and significant.

The IPCC doesn't say "we're all going to die" and it doesn't say "it'll be fine." It says the risks are serious, the range of outcomes is wide depending on policy choices made in this decade, and the window for limiting the worst outcomes is narrowing. That's actually a meaningful and specific statement if you read it carefully, even if it sounds like diplomatic mush when summarized.

What the IPCC Reports Actually Say (and Don't Say)

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