Climate change: what science has established and what changes for Brazil

Few scientific conclusions have been tested as exhaustively as this one: the planet has warmed by about 1.2 °C since the pre-industrial era, and human activity is the dominant cause of that warming. The IPCC, the United Nations climate panel that brings together thousands of scientists, deems human influence on climate unequivocal. In the research community, the debate over whether warming exists and who caused it ended years ago. The remaining questions are different — and they pertain directly to Brazil’s future.

A physics theory nearly two centuries old

Contrary to the impression of a recent topic, the science behind global warming is old. As early as the 19th century, researchers such as Joseph Fourier, Eunice Foote, John Tyndall and Svante Arrhenius described the greenhouse effect: certain atmospheric gases, like carbon dioxide and water vapor, let sunlight in but trap part of the heat the Earth radiates back to space. Without this natural blanket, the planet would be a frozen ball. Arrhenius even calculated, in 1896, that doubling CO₂ concentration would raise global temperature by a few degrees — an estimate remarkably close to modern science.

Since the late 1950s, the Mauna Loa Observatory in Hawaii has continuously recorded atmospheric CO₂, producing the famous Keeling Curve — a line that only goes up. Concentrations have risen from about 280 ppm in the pre-industrial era to over 420 ppm today, the highest level in hundreds of thousands of years, as trapped air bubbles in Antarctic ice show. Moreover, the chemical signature of this extra carbon points to a specific source: the burning of fossil fuels.

How we know — and what is still debated

Scientific confidence does not stem from a single measurement but from the convergence of independent lines of evidence. Surface thermometers, satellites, ocean buoys, retreating glaciers, Arctic melt and sea-level rise — about 20 cm since the end of the 19th century — all tell the same story. The oceans, which absorb the overwhelming majority of the extra heat trapped by the greenhouse effect, warm consistently from the surface to the depths.

There are also the fingerprints of the phenomenon. If the Sun were responsible, the entire atmosphere would warm together; what we observe is the surface heating while the stratosphere cools — exactly the pattern predicted for greenhouse-gas-driven warming. Nights warm faster than days — another sign of the same signature.

That does not mean everything is settled. The research frontier debates the exact climate sensitivity, cloud behavior, the rate of melting of the great ice sheets and the so-called tipping points — thresholds beyond which changes become irreversible on a human-life timescale. Distinguishing what is consensus from what is frontier is scientific honesty. Yet the warning stands: uncertainty is not synonymous with comfort. It cuts both ways — scenarios may turn out better or worse than expected.

What this means for Brazil

Amazon: the continent’s water pump

The Amazon rainforest is not only a massive carbon stock; it is a rain-recycling machine. The trees pump moisture into the atmosphere, feeding the so-called “flying rivers” — air currents laden with vapor that help irrigate the Central West, the Southeast and even neighboring countries. Brazilian scientists have warned for decades that the combination of deforestation and warming could push parts of the forest past a tipping point, where the degraded ecosystem begins to resemble a savanna. If that happens, the loss will not be purely environmental: it will affect the water supply of regions that host a large share of the nation’s population and economy.

Agribusiness: a rain-powered powerhouse

Brazil has become one of the world’s largest food producers largely by relying on rain-fed agriculture, dependent on regular rainfall. Changes in precipitation patterns directly affect soy, corn, coffee and pastures, and already force researchers to redraw agricultural zoning. The northeastern semi-arid region, one of the planet’s most populous dry areas, is among the zones identified as most vulnerable to increasing aridity.

Energy: the strength and weakness of hydroelectric power

Brazil’s power matrix is largely renewable, a rare asset among major economies — but heavily reliant on hydroelectric plants. Severe droughts have already forced the country to fire up expensive, polluting thermal plants to compensate for low reservoirs, raising electricity bills for everyone. A more volatile climate makes this a structural risk, and explains the push for diversification with solar and wind energy, which are abundant especially in the Northeast.

Cities and health: where climate meets people

For most Brazilians, climate change manifests as extreme events: heavier, more concentrated rainfall that turns inhabited slopes into recurrent disaster zones, floods that paralyze megacities, heatwaves that especially strike the elderly and outdoor workers. Science has established that a warmer atmosphere holds more water vapor, intensifying storms. Add the spread of mosquito-borne diseases such as dengue, favored by higher temperatures, and sea-level pressure on coastal cities, and the picture is clear: adaptation is no longer optional.

Mitigation and adaptation: the two halves of the response

The response to the problem has two arms. The first is mitigation: cutting emissions to limit warming, a goal enshrined in the Paris Agreement, which seeks to keep temperature rise well below 2 °C, with an effort to stay at 1.5 °C. Brazil has a peculiar profile: unlike major industrial economies, the largest share of its national emissions comes from deforestation and land-use change, not from fuel combustion. In other words, the cheapest and most effective climate policy within the country’s reach is to keep the forest standing.

The second arm is adaptation: disaster-alert systems, urban drainage, housing outside risk zones, rural insurance, drought-resistant crops, infrastructure designed for the climate we will have, not for the one we had. Every real invested in prevention usually saves many more in reconstruction — a calculation that Brazilian municipalities know all too well.

The climate we will leave as a legacy

Science has done its part: it has established the cause, measured the speed and mapped the risks with a degree of confidence that few fields of knowledge achieve. What remains is not a scientific doubt but a collective choice — of policy, economics and priority. For Brazil, this choice is even sharper: few countries combine such climate vulnerability with such influence, thanks to the Amazon, the renewable-heavy energy mix and the strength of its agricultural sector. Every fraction of a degree avoided means fewer hillside tragedies, greater food-production security and more stable electricity bills. The future of global climate inevitably passes through Brazilian territory — and that is a responsibility no generation can hand back.