# Proof Narrative: The climate has always changed — today's warming is not unusual or alarming.

## Verdict

**Verdict: PARTIALLY VERIFIED**

One part of this claim is true, one part is contradicted by overwhelming evidence, and one part is unanswerable by science alone.

## What was claimed?

The claim is a common argument in climate debates: because Earth's climate has always shifted naturally — through ice ages, warm periods, and everything in between — the warming happening today is nothing special and nothing to worry about. The implication is that current change is just more of the same natural variation. This matters because if true, it would undercut the case for taking costly or disruptive action on climate change.

## What did we find?

The first part of the claim — that Earth's climate has always changed — is simply true, and not in dispute among scientists. NASA and NOAA both document a long history of natural climate variability. Ice ages, warm interglacials, and regional warm spells like the Medieval Warm Period are all part of the geological record. Nobody is arguing that today's climate change is the first change Earth has ever experienced.

The problem is what the claim does next: it implies that because past changes happened, today's change is therefore unremarkable. This is where the evidence turns sharply against the claim.

The question that actually matters is not whether climate has changed before — it's *how fast* it's changing now compared to those past episodes. And here, three independent sources using different data and methods reach the same conclusion. NASA reports that current warming is occurring roughly ten times faster than the average rate of recovery warming after the last ice age. The IPCC Sixth Assessment Report — synthesizing thousands of peer-reviewed studies from scientists across 66 countries — found that key climate indicators "are changing at rates unprecedented in at least the last 2,000 years." A University of Arizona paleoclimate study, drawing on ice cores, ocean sediments, and tree rings covering 24,000 years, found that "the speed of human-caused global warming is faster than anything we've seen in that same time."

It's worth addressing the two most common counterarguments directly. The Medieval Warm Period is sometimes cited as evidence that today's warmth is unremarkable. But that event was regional, not global, and its peak temperatures were lower than today's. More importantly, it unfolded over centuries — not decades. The same applies to the Holocene Thermal Maximum roughly 6,500 years ago, which was perhaps 0.7°C warmer than pre-industrial baselines but took thousands of years to develop. The current warming of more than 1.3°C has occurred in about 150 years. The *rate* is the key metric, and by that measure, today's warming stands apart from anything in the paleoclimate record.

As for whether today's warming is "alarming" — that's a question science can't answer by itself. Whether a given level of risk warrants alarm depends on values, what you stand to lose, and how you weigh present costs against future harms. Reasonable people can weigh those differently, and no measurement or study can resolve it.

## What should you keep in mind?

The central limitation of this claim is logical, not empirical: the fact that past changes happened naturally does not tell you anything about whether the current change is human-caused or unprecedented in speed. These are separate questions, and the evidence addresses each independently.

One citation in the supporting evidence — a Carbon Brief article quoting the IPCC AR6 — comes from a climate media outlet rather than a primary scientific institution. However, the quoted language is from the IPCC report itself, and the conclusion is independently supported by NASA and the University of Arizona, so the overall finding doesn't rest on that source alone. One additional NOAA source could not be verified because the exact text couldn't be located on the page — but again, it wasn't needed to meet the evidentiary threshold.

Paleoclimate measurements have real limitations: records from thousands of years ago are reconstructed from proxies and have lower time resolution than modern instruments, which means brief spikes might be invisible to us. The IPCC explicitly accounted for this uncertainty in its analysis and still reached its conclusion with high confidence.

## How was this verified?

This claim was broken into three specific sub-claims, each evaluated against a defined evidence threshold using live-fetched citations from government, intergovernmental, and academic sources. You can read the full findings in [the structured proof report](proof.md), examine every citation and methodology decision in [the full verification audit](proof_audit.md), or [re-run the proof yourself](proof.py).