six degrees our future on a hotter planet

Ocean acidification from excess atmospheric carbon dioxide is increasingly lethal to ocean life such as coral reefs.

The numeric limit is thought to be 4,000 cubic kilometers of runoff water consumed per year the current number is 2,600. In the world’s rivers, “the blue arteries of the living planet,” there are 800,000 dams with two new large ones built every day. Increasing droughts from global warming will make the problem ever worse. “Already 85% of the Earth’s ice-free land is fragmented or substantially affected by human activity.” The danger point is 15% of land being used for row crops we’re currently at 12%. Every bit of natural landscape lost threatens ecosystem services like clean water and air and atmospheric carbon balance. Other quantifiable boundaries have yet to be exceeded, but we’re close. We need to reduce the amount of atmospheric nitrogen we fix per year to 35 million tons we’re currently at 121 million tons. With the invention a century ago of the Haber-Bosch process for creating nitrogen fertilizer, we doubled the terrestrial nitrogen cycle. “The entire human economy must become carbon neutral by 2050 and carbon negative thereafter.” 3. Long-term stability requires 350 parts per million (ppm) of carbon dioxide in the atmosphere we’re currently at 391 ppm and rising fast. Global warming is the most overwhelming boundary. Currently we lose over 100 species per million per year.

The boundary is 10 species going extinct per million per year. Loss of biodiversity reduces every form of ecological resilience. Drawing on a landmark paper in Nature in 2009 (“ A Safe Operating Space for Humanity,” by Johan Rockström et al.) Lynas outlined the nine boundaries we should stay within, starting with three we’ve already crossed. Some of those global alterations made by humans may be approaching tipping points-thresholds-that could destabilize the whole Earth system. Welcome to the Anthropocene, our very uniquely human geological era.” We’ve raised the temperature of the Earth system, reduced the alkalinity of the oceans, altered the chemistry of the atmosphere, changed the reflectivity of the planet, hugely affected the distribution of freshwater, and killed off many of the species that share the planet with us. In doing this we’ve had to capture between a quarter and a third of the entire photosynthetic production of the planet. In half a million years we’ve gone from prodding anthills with sticks to building a worldwide digital communications network.

We’ve made a bit of a comeback since then. We were down to just a thousand or so embattled breeding pairs. “About 74,000 years ago,” Lynas began, “a volcanic event nearly wiped out humanity.

Six degrees our future on a hotter planet