Winston Churchill is credited with the expression, “Never let a good crisis go to waste.” The climate crisis surely qualifies.   The energy we release and harness by burning fossil fuels comes from ancient photosynthesis, the metabolic process by which plants and plankton use solar energy to remove carbon dioxide from the earth’s atmosphere, combine it with water, and store it in the form of carbohydrates. Fossil fuel formation required geological processes to bury those carbohydrates so that millions of years of subterranean heat and pressure could slowly turn them into more stable carbon compounds including coal, oil and natural gas.  In a geological blink of an eye, we’ve rapidly reversed that process, burning billions of tons of fossil carbon to produce energy, carbon dioxide and water vapor. That reversal underpins the extraordinary economic growth that humanity has experienced since the industrial revolution — and it’s the cause of our runaway climate crisis.   We still have a window of opportunity to decouple economic growth from fossil fuel combustion, but the evidence is clear that our window is closing, with disastrous consequences. We must change course quickly.   Unfortunately, the upcoming Conference of Parties to the United Nations Framework Convention on Climate Change — the 29th of these annual conferences — seems likely to come and go with little effect. But we can neither afford to wait nor to waver.  In recent years, Britain has led the way in decarbonizing the power sector. Other nations have led on transportation and land use. The challenge of rapidly and radically reducing global greenhouse gas emissions from every economic sector is enormous. Thankfully it has already begun, but unprecedented acceleration is needed.  While the impacts of the climate crisis are most tangibly felt by people in the form of what we still call “natural” disasters, the science is increasingly clear that our fossil emissions are now a main causal driver of heat waves, droughts and fires, as well as increasing severity of hurricanes, intense storms and flooding. If we look deeper, the consequences for our future are both profound and troubling.  The capacity of core elements of the earth system to buffer the impacts of our rapid, massive transfer of fossil carbon to the atmosphere now appears to be overwhelmed. Surface sea temperatures are a case in point.   We’ve depended on the oceans to store most of the excess heat at the earth’s surface, but since March of last year, sea surface temperatures have gone off the charts, and have remained substantially elevated above records set during the past 35 years. The power of recent Hurricanes Helene and Milton derived from the unusually high temperature of surface water in the Gulf of Mexico — a manifestation of this phenomenon.  Another major buffer for the earth’s climate system is the net absorption of carbon by terrestrial and marine ecosystems.   Less than half of the fossil carbon that we’ve emitted since the industrial revolution has remained in the atmosphere. Most of the rest has been absorbed by land plants and remained in plants and soils. Less has been absorbed by the oceans — some in plants and animals, most in the water column itself — which has led to the oceans becoming slightly more acidic, since water and carbon dioxide combine to form weak carbonic acid. But land and ocean “carbon sinks” shrank considerably last year, as evidenced by an annual increase in atmospheric carbon roughly five times the increase in fossil emissions.  The aggregate result is that the planet is heating faster than anticipated, with worse impacts on people and the natural ecosystems we depend on. We have already exceeded the 1.5 degree threshold agreed upon by international scientists and policymakers alike. Both the weakening of oceanic heat absorption and the reduction in nature’s carbon sinks are likely due to impacts of the fossil fuel-driven climate crisis itself. On land, we’ve seen those impacts most palpably in record-setting fires across the globe, driven by heat and drought.  The window of opportunity we have requires not only decarbonization but unprecedented investment in the protection and strengthening of the Earth’s natural buffers against the impacts of the climate crisis: our forests, peatlands, grasslands and marine ecosystems. This investment must include support for Indigenous peoples and other communities whose stewardship underpins the ecological integrity of nature. And we must own and repair our broken relationship with nature, including restoring the atmosphere to healthy and sustainable levels of greenhouse gases by both biological and technological means.  Critically, we need to face facts. We are living on a planet already hotter and more unstable than at any time in human history. Pretending otherwise will only perpetuate and worsen human suffering and the demise of nature.   Daniel Zarin is executive director of the Forests and Climate Change Program at Wildlife Conservation Society.