Climate Change: What the Data Shows, Why It Became Political, and What's Still Debated

The One-Sentence Version

The Earth is warming, CO2 levels are higher than at any point in 800,000 years of ice core records, and every major scientific body in every major country attributes the warming primarily to human activity. How this became a partisan issue is a separate question from whether it’s happening.

How It Works

The Sun’s energy passes through the atmosphere and heats the Earth’s surface. The Earth then radiates heat (infrared radiation) back toward space. Certain gas molecules in the atmosphere — primarily carbon dioxide, methane, and water vapor — absorb some of that outgoing heat and re-emit it in all directions, including back toward the surface. This is the greenhouse effect.

Without it, Earth would be roughly -18°C (0°F). The greenhouse effect is natural and necessary. The concern is about intensifying it by adding greenhouse gases faster than the natural system has experienced in at least 800,000 years.

The Measurements

Carbon dioxide

For at least 800,000 years — based on air bubbles trapped in Antarctic ice cores — CO2 concentrations fluctuated between 180 ppm during ice ages and roughly 300 ppm during warm interglacial periods. The highest value in that entire 800,000-year record was 298.6 ppm.

The current level is approximately 430 ppm — 54% higher than pre-industrial levels. The rate of increase is 100 to 200 times faster than the fastest natural increases at the end of the last ice age. The Mauna Loa Observatory in Hawaii has measured atmospheric CO2 continuously since 1958, producing a record known as the Keeling Curve. It shows an unbroken upward trend from 315 ppm to 430 ppm over 67 years. Ice core data extends the record back 800,000 years. No comparable rate of increase appears anywhere in that record.

Temperature

The global average temperature has risen approximately 1.3-1.5°C (2.3-2.7°F) since the pre-industrial period (1850-1900). Four independent research groups track this using different methods and data sources:

Dataset	Institution	Key Feature
GISTEMP	NASA Goddard Institute	Uses ~25,000 weather stations
GlobalTemp	NOAA	Independent methodology from NASA
HadCRUT	UK Met Office / University of East Anglia	Longest-running record
Berkeley Earth	Independent nonprofit	Uses ~39,000 records; extends land data to 1701

All four show approximately the same warming trend. If any single dataset had a systematic error, the others would diverge from it. They don’t. 2024 was the hottest year in the 146-year instrumental record. 2023 was the second hottest. 2025 was the third. The ten warmest years on record have all occurred since 2010.

Sea level

Since 1993, when satellite altimetry began providing precise measurements, global sea level has risen approximately 111mm (4.4 inches). The rate has more than doubled — from 2.1 mm/year in the early satellite era to 4.5 mm/year currently. Short-term fluctuations from El Niño and La Niña cycles are normal; the long-term trend is upward.

Arctic ice

Satellite observations since 1979 show September Arctic sea ice shrinking at 12.2% per decade. The average minimum extent has declined from 6.85 million km² (1979-1992) to 4.44 million km² (2007-2020). The 18 lowest minimums have all occurred in the last 18 years.

Ocean chemistry

The ocean absorbs roughly 25-30% of human CO2 emissions. When CO2 dissolves in seawater, it forms carbonic acid. Since the industrial revolution, ocean pH has dropped from approximately 8.2 to 8.1. Because the pH scale is logarithmic, this represents a 30% increase in acidity. Coral growth in the Great Barrier Reef has declined 14% since 1990.

The satellite temperature question

Two groups analyze satellite microwave data for atmospheric temperatures: UAH (University of Alabama-Huntsville) and RSS (Remote Sensing Systems). For years, UAH showed less warming than surface records, and skeptics cited it as evidence that surface measurements were wrong. The discrepancy turned out to be a calibration issue — satellite orbits drift over time, and different correction methods produced different results. Weather balloon data, an independent measurement, confirmed warming consistent with RSS and surface records.

What’s Settled and What’s Not

Settled in the scientific literature

CO2 and other greenhouse gases trap heat. This is basic physics, confirmed experimentally since 1859.
Human activities have increased atmospheric CO2 from ~280 to ~430 ppm.
The planet has warmed approximately 1.3-1.5°C since pre-industrial times.
Humans are the dominant cause of warming since 1950. The IPCC’s 2021 report: “It is unequivocal that human influence has warmed the atmosphere, ocean and land.”
Sea levels are rising, ice sheets are shrinking, and oceans are acidifying.

Open scientific questions

Climate sensitivity: How much warming results from a doubling of CO2? The IPCC estimates 2.5-4.0°C, but the range has been hard to narrow.
Cloud feedbacks: Whether clouds will amplify or dampen warming remains the single largest source of uncertainty.
Tipping points: Whether systems like the Atlantic Ocean circulation or West Antarctic Ice Sheet might undergo abrupt, irreversible changes.
Regional projections: Global trends are clear; predicting specific regional impacts carries much larger uncertainty.

The fundamental question — whether the planet is warming due to human CO2 emissions — is settled. The open questions involve magnitude, speed, and regional distribution.

The “97% consensus”

Multiple independent studies have found that approximately 97% of actively publishing climate scientists agree that human activities are causing significant warming. The most cited is Cook et al. (2013), which examined 11,944 peer-reviewed abstracts.

The methodology has drawn criticism. Richard Tol challenged the approach, arguing it lacked proper controls. Two-thirds of the abstracts examined expressed no position on human causation — the 97% applies only to the one-third that did. The definition of “endorsement” was broad enough to include varying levels of agreement.

The specific number depends on methodology. The direction does not. Every study — including those conducted by skeptics — finds that the vast majority of actively publishing climate scientists agree on human causation. A 2021 analysis of 88,125 climate-related studies found over 99.9% agreement. Every national academy of sciences in every major country has issued statements acknowledging human-caused climate change. No national scientific body disputes it.

Common Objections

”The climate has always changed”

Ice ages, warm periods, and everything in between are part of Earth’s history. The question is about rate. The transition out of the last ice age involved 4-5°C of warming over approximately 7,000 years. Current warming is producing comparable change in a fraction of that time. CO2 has risen 54% in 200 years; during ice age transitions, comparable changes took thousands of years.

The Royal Society: “The speed of the current climate change is faster than most of the past events, making it more difficult for human societies and the natural world to adapt."

"It’s the sun”

Satellites have measured total solar irradiance directly since 1978. The data shows no upward trend. Solar brightness varies by less than 0.1% over solar cycles. NASA estimates solar changes account for approximately 0.01°C — about 1% — of observed warming since the industrial era.

A diagnostic distinction exists in the data: if the sun were causing warming, both the lower atmosphere (troposphere) and upper atmosphere (stratosphere) would warm together. Observations show the troposphere warming while the stratosphere cools — a pattern consistent with greenhouse gas trapping rather than solar heating.

”Climate models are unreliable”

A 2020 study in Geophysical Research Letters evaluated 17 climate model projections published between 1970 and 2007. Fourteen of the seventeen were consistent with what actually occurred when adjusted for actual emissions. James Hansen’s 1988 model predicted approximately 0.6°C of warming from 1988-2017. The actual warming was approximately 0.6°C.

Models perform better at global trends than regional specifics. They struggle most with clouds, precipitation patterns, and extreme weather frequency. The core prediction — more CO2 leads to a warmer planet — has been consistent across models and validated against observed temperatures over several decades.

”It was warmer during the Medieval Warm Period”

The Medieval Warm Period (roughly 950-1250 CE) was real, but it was primarily a regional phenomenon concentrated in the North Atlantic and parts of Europe. Peak warmth occurred at different times in different regions. The IPCC’s global temperature reconstruction shows current temperatures exceeding those of the Medieval Warm Period, though paleoclimate data involves genuine uncertainties and the MWP’s spatial extent remains an active area of research among paleoclimatologists.

”CO2 is plant food”

In controlled laboratory conditions, elevated CO2 can increase growth in some plant species. Field conditions introduce additional variables. Heat stress overwhelms the fertilization benefit when temperatures exceed a crop’s optimum range. Elevated CO2 also reduces the nutritional content of crops — more biomass, but lower concentrations of protein, minerals, and vitamins. A 2025 systematic review found that without adaptation, climate change could reduce global agricultural production by up to 14% by 2050.

”China and India emit more, so why should we act?”

China leads in annual emissions at 13.26 gigatons (2023-24). The U.S. is second at 4.68 gigatons. India is third at 2.96 gigatons. Per capita, Americans emit approximately 13.8 tonnes — about 50% more than Chinese citizens and roughly 6.7 times more than Indians. Cumulatively, the United States has emitted more CO2 than any other country — approximately one-quarter of all historical emissions.

”The economy can’t afford it”

Bjorn Lomborg, a political scientist and author of The Skeptical Environmentalist, argues that the costs of current climate policies “vastly outweigh” the costs of climate change itself, and that R&D investment in cheaper clean energy would be more efficient than emissions mandates.

The Stern Review (2006) estimated the cost of inaction at 5-20% of global GDP annually, indefinitely, while the cost of action would be approximately 1-2% of GDP. A 2024 ETH Zurich/IIASA study estimated that 3°C of warming could decrease global GDP by up to 10%.

On the cost side, the energy market has shifted. Solar and wind are now the cheapest forms of new electricity generation for the tenth consecutive year (Lazard, 2025). In 2024, 91% of new renewable projects globally came in cheaper than any fossil fuel alternative.

Source	Cost Range ($/kWh)
Onshore wind	$0.037 - $0.086
Utility-scale solar	$0.038 - $0.217
Gas combined cycle	$0.048 - $0.109
Coal	$0.071 - $0.173

”Bill Gates walked this back”

In October 2025, Gates published a memo arguing against the “doomsday view” of climate change. The widely shared quote: “Fortunately for all of us, this view is wrong. Although climate change will have serious consequences — particularly for people in the poorest countries — it will not lead to humanity’s demise.”

In the same memo, Gates wrote: “Climate change is a very important problem. It needs to be solved.” He argued for shifting emphasis from emergency rhetoric to pragmatic solutions. His $4 billion climate venture fund remained active as of 2026. He did not retract any scientific claim.

”Scientists have admitted they were wrong”

Patrick Brown (2023) published a wildfire study in Nature, then claimed he’d omitted other factors because journals only publish papers fitting a “preapproved narrative.” Brown explicitly stated climate change’s influence on wildfires is “very real.” Peer review records showed reviewers had already flagged the omissions he claimed would have prevented publication. Nature’s editor-in-chief rejected his claims.

Climategate (2009): Stolen emails from the University of East Anglia were presented as evidence of data manipulation. Nine separate investigations — UK Parliament, Penn State, NOAA IG, NSF IG, EPA, and others — all exonerated the scientists. No fraud was found.

Individual skeptic scientists frequently cited (Lindzen, Curry, Clauser) either never accepted the consensus, argue about uncertainty ranges rather than the basic science, or have no publications in climate science. John Clauser’s 2022 Nobel Prize was for quantum entanglement experiments. A 2021 analysis of 88,125 climate-related studies found over 99.9% agreement on human causation.

The IPCC has strengthened its language with every successive report — from “a discernible human influence” (1995) to “unequivocal” (2021).

How It Became Political

The bipartisan era

Environmental protection was not always a partisan issue.

1970: Richard Nixon (R) created the EPA. The Clean Air Act passed the Senate 73-0.
1988: George H.W. Bush (R) campaigned on climate change.
1992: Bush signed the UN Framework Convention on Climate Change.
2008: John McCain (R) ran on a cap-and-trade platform.

The shift

1997: The Senate voted 95-0 against any climate treaty that exempted developing nations.

2001: George W. Bush withdrew from the Kyoto Protocol.

2002: Republican strategist Frank Luntz wrote an internal memo advising: “The scientific debate is closing [against us] but not yet closed… continue to make the lack of scientific certainty a primary issue in the debate.” He recommended replacing “global warming” with “climate change” as a “less frightening” phrase. Luntz later recanted publicly.

What Exxon knew

Internal documents reveal that Exxon’s own scientists understood the connection between fossil fuels and climate change decades ago. In 1977, senior scientist James Black told management that fossil fuel burning was influencing global climate. In 1978, Black warned that doubling CO2 would increase temperatures by 2-3°C — consistent with today’s consensus. Exxon’s internal models turned out to be 63-83% accurate compared to actual temperatures (Harvard/Science, 2023).

Despite this, Exxon spent more than $30 million funding think tanks that promoted doubt. An internal memo from a fossil fuel coalition stated the goal: “Victory will be achieved when the average person is uncertain about climate science.”

The funding network

Koch Industries has directed over $100 million since 1997 to organizations promoting doubt about climate science, including the Heartland Institute and Americans for Prosperity. These organizations produce reports cited by politicians as evidence of scientific disagreement. This is documented through internal memos, tax filings, and investigative reporting from the Los Angeles Times, Inside Climate News, and the Columbia Journalism School.

Where It Stands Now

Policy

In February 2026, the Trump administration revoked the EPA’s Endangerment Finding — the scientific determination that greenhouse gases endanger public health. This removed the legal foundation for all federal climate regulation under the Clean Air Act: vehicle emissions standards, power plant limits, methane regulations, and greenhouse gas reporting. Eighteen states filed lawsuits immediately. The case is expected to reach the Supreme Court.

Additional actions in 2025-2026 include loosening mercury and arsenic regulations, using $982 million in taxpayer funds to cancel offshore wind projects, and proposing 52% EPA budget cuts.

Conservative support for climate action

Support for addressing climate change extends beyond the Democratic Party. Bob Inglis, a former Republican congressman, leads RepublicEn, advocating a revenue-neutral carbon tax. George Shultz (Reagan’s Secretary of State) and Henry Paulson (Bush’s Treasury Secretary) both supported market-based carbon pricing. The U.S. military has called climate change a “threat multiplier” since 2014 — of 79 installations reviewed, 53 face recurrent flooding, 43 drought, and 36 wildfire risk.

The insurance industry provides independent evidence. Insurers have no political incentive to exaggerate climate risk but a financial incentive to price it accurately. Insured losses from natural catastrophes have exceeded $100 billion for six consecutive years. Munich Re identified climate change as a factor intensifying losses in its 2025 report.

Energy and jobs

The U.S. clean energy workforce reached 3.56 million jobs in 2024, growing three times faster than the overall economy. Wind turbine technician is projected to be the fastest-growing occupation through 2034 (50% growth), followed by solar PV installer (42%). Only 8 states have more fossil fuel workers than clean energy workers.

NOAA’s database of billion-dollar weather disasters shows $2.9+ trillion in cumulative U.S. costs from 1980-2024, with an average of $140 billion per year over the last decade.

Sources

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Scientific assessments:

Objections addressed:

Politicization:

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