On September 26, 2013, the World's Top Climate Scientists Declared Human-Caused Warming 'Extremely Likely'
On September 26, 2013, the Intergovernmental Panel on Climate Change released the first installment of its Fifth Assessment Report in Stockholm, Sweden, delivering the most confident scientific statement yet on humanity's role in a warming planet. After years of data collection, peer review, and diplomatic wrangling among hundreds of scientists from dozens of countries, the panel concluded that it was "extremely likely" — meaning at least 95 percent probability — that human activity was the dominant cause of global warming since the mid-20th century. The figure marked a jump from the 90 percent certainty cited in the panel's previous report in 2007, and it landed at a moment when public debate over climate science remained fierce.
The 95 Percent
The report's authors, drawn from more than 800 scientists working across nine years of research, synthesized findings from more than 9,200 peer-reviewed studies. Their conclusion rested on multiple independent lines of evidence: rising ocean temperatures, shrinking Arctic sea ice, accelerating glacier melt, and a well-documented rise in atmospheric carbon dioxide tied directly to fossil fuel combustion. Thomas Stocker, co-chair of the working group that produced the report, told reporters in Stockholm that continued emissions would cause "further warming and changes in all components of the climate system," language deliberately calibrated to avoid overstatement while still conveying urgency. The panel's Nobel Prize-winning credibility — shared with Al Gore in 2007 — gave the findings institutional weight that few scientific bodies could match, even as the report itself acknowledged lingering uncertainties in exactly how fast some changes would unfold.
Reaction split along familiar lines almost immediately. Environmental groups and many governments treated the 95 percent figure as a call to action ahead of the Paris climate negotiations still two years away, while skeptics in the U.S. Congress and elsewhere questioned the models underpinning the projections. What neither side disputed was the scale of the undertaking: the report ran to thousands of pages, condensed into a 36-page summary for policymakers that took a marathon overnight session to finalize word by word. That summary would go on to become one of the most cited documents in modern environmental policy, a single number — 95 percent — doing the work of a decade's worth of data.
















