The most commonly cited target in international climate negotiations is that we ought to limit warming to an average of 2°C. However, that may already be too high.
How to shrink a city: this will become an increasing issue in many parts of the world due to likely demographic and economic changes of the next few decades.
Peak oil and healthcare, a UK perspective.
Terminological clarification: irreversible vs unstoppable.
Hot Topic: On giving up non-essential flying.
The health benefit of more ambitious emissions targets. If Europe raised its sights from 20% to 30% emissions cuts by 2020, then it could be saving an extra €30 billion per year in health costs. This saving alone would account for a significant portion of the estimated €46 billion p.a. the higher target would require.
Twenty-two percent of the world's plant species are threatened with extinction and another thirty-three percent have an unknown status. The main culprit? Land use changes associated with agriculture.
Rivers in peril worldwide: study in Nature claims that eighty percent of the world's population (nearly 5.5 billion people) lives in an area where rivers are seriously threatened. "[S]ome of the highest threat levels in the world are in the United States and Europe." See also here a graphic of the threat distribution.
Oceans acidifying much faster than ever before in Earth's history.
Soil degradation, erosion and desertification continues in many places around the world, reducing the amount of arable land.
On average, every single man, woman and child on the planet is US$28,000 in debt.
Speaking of money, a new study has estimated that the cost of vanishing rainforest each year is approximately US$5 trillion (with a "t". i.e. US$5,000,000,000,000).
However, the real issue is that each of these crises are not isolated, but are all converging on similar time scales.