Independent measurements made at the beginning of May by the US National Oceanic and Atmospheric Administration showed that global atmospheric concentrations of carbon dioxide, as measured atop Hawaii's Mauna Loa volcano, reached 400 parts per million (ppm). This means that CO2 concentration is rapidly and dangerously approaching the threshold of 450 ppm, set as the UN's goal to contain global warming within 2° above manageable effects.

Beyond this threshold, a series of potentially irreversible phenomena could be triggered and the effects of climate change could become catastrophic.

Scientists recalled that the last time in the earth's history we saw similar levels of CO2 was probably about 4.5 million years ago when the world was warmer than today by 3 or 4° Celsius, there was no permanent ice sheet on Greenland, sea levels were much higher, and the world was a very different place.

For our world, this warming scenario will likely mean that hundreds of millions of people will be displaced from their homelands in the near future, as climate change economist Stern pointed out. "When temperatures rise to that level, we will have disrupted weather patterns and spreading deserts," he said. "Hundreds of millions of people will be forced to leave their homelands because their crops and animals will have died. The trouble will come when they try to migrate into new lands, however. That will bring them into armed conflict with people already living there. Nor will it be an occasional occurrence. It could become a permanent feature of life on Earth."

For more information please visit the NOAA website.