Climate Change: Both Sides, Real Data

Before We Start

How we're approaching this one

Climate change is one of the most politically charged topics in public life. This newsletter is not going to tell you what to think or what policies to support. What it will do is lay out the measurable data, the strongest arguments on each side, and what the evidence actually says about those arguments. You can decide what to do with that. Every claim here is sourced. Where science is genuinely uncertain, we'll say so.

What We Can Measure

The numbers that don't depend on any model or prediction

Before getting into causes or policy, here are the measurements. These aren't projections. They're readings from instruments, satellites, ocean buoys, and ice cores. They're the agreed-upon starting point for the entire debate.

According to the Copernicus Climate Change Service (the European Union's official climate monitoring program), 2025 was the third-warmest year ever recorded. 2024 was the warmest. 2023 was the second warmest. The last eleven years — 2015 through 2025 — are the eleven warmest years in the entire recorded history of global temperature measurement, which goes back to 1850.

1.47°Caverage global temperature rise above pre-industrial levels in 2025 (Copernicus/ECMWF)

11 for 11the last 11 years (2015–2025) are all in the top 11 warmest years ever recorded

22 of 34of Earth's tracked vital climate signs are at record levels, per the 2025 State of the Climate report

Beyond temperature, other independently measured indicators include: sea level riseSea level is measured by satellite altimeters and coastal tide gauges. It has risen roughly 20 centimeters (about 8 inches) since 1900, with the rate of rise accelerating since the 1990s. The causes are thermal expansion (warmer water takes up more space) and melting ice adding water to the ocean. Both are measurable and have been measured independently by multiple countries' satellite programs. reaching record highs in 2025; cumulative glacier and Greenland ice sheet loss hitting a new record high; CO2 concentrationsCO2 is measured directly from the atmosphere at monitoring stations worldwide, most famously at the Mauna Loa Observatory in Hawaii (continuously since 1958). Current CO2 levels are approximately 424 parts per million — the highest in at least 800,000 years, based on measurements from Antarctic ice cores that trap ancient air bubbles. Pre-industrial CO2 was approximately 280 ppm. The rise tracks almost perfectly with the industrialization timeline. reaching record levels; and Arctic sea ice recording its lowest winter peak ever.

These measurements are collected by NASA, NOAA, ESA (European Space Agency), and dozens of independent national science agencies. They agree with each other to within measurement error margins.

The Mainstream Scientific Case

What the scientific consensus actually says — and why

The IPCC Sixth Assessment Report — the most comprehensive review of climate science ever conducted — concluded that human influence warming the planet is "unequivocal." Here's the core argument.

The mechanism is well understood: certain gases in the atmosphere — primarily CO2, methane, and nitrous oxide — trap heat that would otherwise radiate back into space. This is called the greenhouse effectThe greenhouse effect is not a theory — it's a physical property of certain molecules that has been understood since the 1850s, when scientist Eunice Newton Foote first demonstrated it in a lab. The same physics is used to design Mars rovers, calculate rocket trajectories, and understand why Venus is hotter than Mercury despite being farther from the Sun. It is not controversial in the scientific sense.. It is not controversial physics. The question the science addresses is how much warming a given amount of CO2 produces — and human emissions have added more CO2 to the atmosphere in 150 years than any previous period took millennia to accumulate.

The key evidence that the warming is human-caused rather than natural: the atmospheric fingerprintGreenhouse gas warming and solar warming produce different patterns in the atmosphere. Greenhouse gas warming warms the lower atmosphere (troposphere) while cooling the upper atmosphere (stratosphere). Solar warming would warm both layers simultaneously. Measurements show the stratosphere is cooling while the troposphere warms — matching the greenhouse gas prediction exactly, not the solar prediction. This "fingerprint" test is one of several lines of evidence pointing specifically to greenhouse gases rather than other causes.. Solar-caused warming and greenhouse gas warming produce different patterns. The observed pattern — lower atmosphere warming, upper atmosphere cooling — matches greenhouse gas warming, not solar forcing.

"Human activity remains the dominant driver of the exceptional temperatures we are observing. Atmospheric greenhouse gases have steadily increased over the last 10 years." — Laurence Rouil, Director of Copernicus Atmosphere Monitoring Service, January 2026

As of 2025, approximately 99.9% of actively publishing climate scientists agree that human activities are the primary driver of recent climate change, according to multiple independent consensus studies. This is not an argument from authority — it's the outcome of the same scientific process that produced vaccines, GPS, and the internet: repeated testing, peer review, and independent replication across hundreds of countries and institutions.

The Skeptical Arguments

The strongest skeptical claims — stated fairly, with the evidence assessed honestly

Skeptical arguments have a hierarchy. The weakest ones deny that warming is happening at all. The strongest ones accept warming but question causes, magnitude, speed, or the wisdom of proposed solutions. We'll focus on the strongest versions because those deserve serious engagement.

Partially true

Claim: "Climate has always changed naturally"

Earth has been warmer and cooler throughout its history. Ice ages, warm periods, and natural cycles are real. This is documented in the geological record.

What the evidence says

True that climate changes naturally. What's different now: the current rate of warming is 10–100 times faster than typical natural variation. The ice core record going back 800,000 years shows no period where CO2 rose this fast. Natural factors (solar, volcanic, orbital cycles) cannot account for the observed warming pattern. They're included in climate models and don't explain it.

Partially true

Claim: "It's the Sun, not humans"

Solar activity drives climate over long timescales. The Sun has gone through cycles throughout history. Some skeptics argue current warming is a solar cycle peak.

What the evidence says

Solar output has actually slightly decreased since the 1980s while temperatures kept rising — moving in opposite directions. Additionally, solar warming would warm all atmospheric layers. The observed pattern (lower atmosphere warming, upper cooling) matches greenhouse warming, not solar. NASA has explicitly addressed this with satellite solar measurements.

Legitimate concern

Claim: "Climate models are uncertain and often wrong"

Climate models make projections decades into the future. Models have been wrong on specific regional predictions. Uncertainty ranges in projections are wide.

What the evidence says

Models do have uncertainty, and the IPCC acknowledges this explicitly. However, 2025 observations were nearly identical to the central estimate of IPCC AR6 model projections — models tracking well. Uncertainty cuts both ways: some projections could be too conservative, not just too aggressive. And uncertainty about exact magnitude doesn't undermine the core warming trend, which is also measured directly.

Valid point

Claim: "CO2 is plant food — more CO2 benefits agriculture and ecosystems"

CO2 does help some plants grow faster. Longer growing seasons in some northern regions are real. Some crops have shown yield increases in controlled CO2 studies.

What the evidence says

This is partly true. CO2 fertilization is real and some plants benefit. However, the research consensus is that negative agricultural impacts — drought, heat stress, shifting precipitation, extreme events, ocean acidification affecting food chains — significantly outweigh the benefits at projected warming levels. The net effect on food security is negative in most scenarios.

Strongest skeptical argument

Claim: "The cure may be worse than the disease — climate policy costs are enormous"

Rapid decarbonization would cost trillions. Energy costs would rise. Developing countries would be hardest hit if denied cheap fossil fuels for growth. Economic disruption could cause more harm than warming itself.

What the evidence says

This is the most legitimate debate in the field — not about whether warming is real, but about the cost-benefit of responses. Economists genuinely disagree. The counterargument: climate damages could reach $38 trillion annually by 2050 without action, and renewable energy is now the cheapest electricity source in most regions. But the distributional effects of rapid transition are a real policy concern that serious economists take seriously.

Where Real Uncertainty Exists

What scientists genuinely don't know — and what that means

One thing mainstream science and legitimate skeptics agree on: there is genuine uncertainty about climate sensitivity — exactly how much warming results from a given amount of CO2 — and what specific regional impacts will look like.

What is not genuinely uncertain: that warming is happening, that CO2 concentrations are at historic highs, that the pattern matches greenhouse gas forcing rather than natural causes, and that the rate of change is unprecedented in the human record. Those are measurements, not models.

Also worth noting: the shift in skeptical arguments over time is itself informative. In the 1990s, the main skeptical argument was "warming isn't happening." By the 2000s it became "it's happening but it's natural." By the 2010s it became "it's happening but models are too sensitive." Today the dominant skeptical position has largely shifted to "the costs of action are too high." That's a policy debate, not a scientific one — and it's a legitimate debate to have.

Quick Rundown

The whole story in five lines

The measurements The last 11 years are the 11 warmest in recorded history. CO2 is at its highest level in 800,000 years. Sea levels, ocean heat, and glacier loss are all at records. These are instrument readings, not model outputs.

The cause The IPCC concluded human influence is "unequivocal." The atmospheric fingerprint — lower atmosphere warming while the upper cools — matches greenhouse gas physics, not solar variation. Solar output has declined since the 1980s while temperatures rose.

Skeptical claims "Climate always changes" is true but doesn't explain the current rate. Solar theories don't match the fingerprint. Model uncertainty is real but cuts both ways. CO2 helping plants is partially true but net agriculture effects are negative.

Real uncertainty Exactly how sensitive the climate is to CO2 doubling. Specific regional impacts. The cost-benefit of various policy responses. These are legitimate open questions — not whether warming is happening or human-caused.

The shift Skeptical arguments have moved from "it's not happening" to "the solutions are too expensive." That's no longer a science debate — it's a policy and economics debate. Both sides have legitimate points on that question.

Sources