The evidence is so overwhelming that it's become almost boring to state. Human activities have unequivocally caused global warming. That's not speculation or projection.
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The evidence is so overwhelming that it's become almost boring to state. Human activities have unequivocally caused global warming. That's not speculation or projection. [1] The Intergovernmental Panel on Climate Change, a United Nations organization, published a Synthesis Report in March 2023 concluding that human activities have unequivocally caused global warming. And the consensus among working scientists is nearly total. [1] More than 99.9 percent of studies agree that humans caused climate change. [2]
But here's what makes this real: greenhouse gases don't work the way most people think. It's not that CO2 is choking the planet. It's that human activities have produced atmospheric gases that trap more of the Sun's energy in the Earth system, warming the atmosphere, ocean, and land. Think of it like closing the windows in a greenhouse. [3] The heat gets in. But now it can't escape. That's the mechanism. And it's happening because of burning fossil fuels and other industrial processes.
Deforestation matters too, in a different way. Humans affect climate by changing the nature of land surfaces, for example by clearing forests for farming. Remove the trees that absorb carbon, and you've doubled the problem. [4] You've eliminated a natural brake on warming while simultaneously releasing more greenhouse gases.
The argument that natural climate cycles might explain what we're seeing doesn't hold up. No other known climate influences have changed enough to account for the observed warming trend. Scientists tested this. [5] They looked at solar cycles, volcanic activity, ocean patterns, all of it. The numbers don't match. Only human greenhouse gas emissions explain what the thermometer is actually showing us.
This consensus isn't abstract. About 97 percent of climate scientists have concluded that human caused climate change is happening based on well established evidence. Among actively publishing climate scientists, the agreement is even stronger. [6] Ninety to one hundred percent agree that carbon dioxide from human activities is warming the planet by making it more difficult for heat to escape the atmosphere. These aren't activists. [7] These are people trained to be skeptical, to demand evidence, to punch holes in each other's work.
The warming isn't theoretical anymore either. We're measuring it. Average global temperatures are rising. Ice sheets and glaciers are melting. Sea levels are climbing. The frequency and intensity of extreme weather events are shifting. These aren't computer models. These are observations from weather stations, satellites, and oceanographic instruments around the world.
When you layer attribution science on top of this, you discover something striking. The tools scientists use to connect causes to effects, to distinguish human warming from natural variability, all point in the same direction.
The story of how we came to understand climate change doesn't start with today's satellites or supercomputers. It starts with a curious Swedish scientist wondering whether the burning of coal might warm the planet.
In 1896, Svante Arrhenius made the first quantitative estimate of climate change induced by carbon dioxide, working through the calculations by hand to explore what would happen if atmospheric CO2 doubled. But the intellectual groundwork went back even further. [8] In the 1860s, John Tyndall's laboratory tests showed that coal gas, containing CO2, was particularly effective at absorbing energy, and he demonstrated that CO2 alone acted like a sponge for sunlight wavelengths. These weren't wild speculations. [9] They were precise experiments showing that certain gases had a hidden power over Earth's heat.
Then in 1938, Guy Callendar published a seminal paper on climate change. He built on Tyndall and Arrhenius, connecting their laboratory findings to what was actually happening in the atmosphere. [10] This work created a bridge between theory and observation that wouldn't fully solidify for decades.
The next leap came from a different angle entirely. By the 1920s, Richardson developed Numerical Weather Prediction, laying the mathematical foundation for modeling the atmosphere itself. This was crucial because you can't understand the whole climate system without the tools to calculate how it behaves. [11] That foundation bore fruit in 1956, when Norman Phillips created the first general circulation model. Then in 1967, Syukuro Manabe and Richard Wetherald published a seminal climate modelling study. [10] These weren't just academic exercises. [10] They showed that scientists could actually simulate the climate—could predict how changing one variable rippled through the entire system.
But simulation meant nothing without data. The breakthrough came from an unlikely source: a young researcher taking precise measurements atop a volcano. Charles David Keeling began continuous measurement of atmospheric CO2 in 1958, leading to the Keeling Curve which has documented daily changes for over six decades. That curve became the iconic proof that atmospheric CO2 was rising steadily, year after year. [12] It was impossible to ignore.
The scientific infrastructure grew to match the scale of the problem. In 1964, the establishment of a modelling group at the National Center for Atmospheric Research in Boulder, Colorado occurred. By the 1970s, the American Petroleum Institute developed a committee called the CO2 and Climate Task Force to monitor climate science developments. [10] This meant the science was gaining attention—serious attention from institutions with stakes in the outcome. [13]
Thanks for listening to this VocaCast briefing. Until next time.