Marcia McNutt is Editor-in-Chief of Science. 2 August 2013. Science: Vol. 341 no. 6145 p. 435
We are not just experiencing increases in greenhouse gas emissions but also eutrophication, pollution of the air and water, massive land conversion, and many other insults, all of which will have interacting and accumulating effects.
The real problem we need to solve in order to truly understand how Earth’s environment may change is that of cumulative impacts.
Although the Paleocene-Eocene Thermal Maximum (about 55 million years ago) is the time period considered to be a reasonable analog to a higher-CO2 future, the planet was not experiencing these other stressors and climate change simultaneously.
Terrestrial species that survive a climate impact alone may face extinction if reduced to a fraction of their natural range through deforestation and habitat fragmentation. Marine species that are mildly susceptible to ocean acidification may not be able to tolerate this condition plus low oxygen levels.
Even the most optimistic predictions are dire.
Environmental changes brought on by climate changes will be too rapid for many species to adapt to, leading to widespread extinctions.
Even species that might tolerate the new environment could nevertheless decline as the ecosystems on which they depend collapse. The oceans will become more stratified and less productive. If such ecosystem problems come to pass, the changes will affect humans in profound ways. The loss in ocean productivity will be detrimental for the 20% of the population that depends on the seas for nutrition. Crops will fail more regularly, especially on land at lower latitudes where food is in shortest supply. This unfavorable environmental state could last for many thousands of years as geologic processes slowly respond to the imbalances created by the release of the fossil carbon reservoir. The time scale for biodiversity to be restored, with all the benefits that it brings, will be even longer.