Something very disturbing happened last month, and it went largely unreported in the world’s mainstream press. On the night of May 2, carbon dioxide levels in the atmosphere touched 400 parts-per-million (ppm) in Hawaii for the first time in at least 800,000 years. Sensors placed near the summit of the volcanic Mauna Loa measured this record on an hourly basis through sunrise the following day. Levels continued near that benchmark throughout May, crossing 400 ppm on May 7th. Scientists say that Arctic weather stations have also hit the hourly 400 ppm mark last spring and this year, but the Mauna Loa station, located at 3,400m and far away from major pollution sources in the Pacific Ocean, has been monitoring levels for more than 50 years and is considered one of the best standards for indicating CO2 levels.

Why is crossing the 400 ppm mark so alarming? Well, scientists had guessed that we would hit the 450 ppm mark some time around this mid-century. It is only 2013, and we have already reached 400 ppm. "At this pace we'll hit 450 ppm within a few decades", said Ralph Keeling, a geologist with the Scripps Institution of Oceanography, which operates the Hawaiian observatory. What is the cause of this rapid increase in carbon dioxide levels in our atmosphere? Carbon dioxide and most of the other greenhouse gases come from industrial and other human activity on the planet, including the burning of fossil fuels (coal, oil and gas) and from deforestation, which has all been steadily on the rise in recent years. Every time we burn fossil fuels, we are adding to the Earth’s emissions of greenhouse gases – and energy use was projected to grow by 50 per cent between 2005 and 2030, hence the rapid increase in CO2 levels.

You might have heard of the global campaign centering on the number 350, to draw attention to 350 ppm which a number of scientists say is the safe upper limit for carbon dioxide (and other greenhouse gases) in the atmosphere. For hundreds of thousands of years, the global atmosphere was fairly stable at around 270-280 ppm of carbon dioxide. Then, two hundred years ago the industrial revolution took place in the West and with the proliferation of smoke emitting factories and coal burning engines we shot up from 280 ppm to 385 ppm and are now touching 400 ppm, which is why the Arctic is melting. Even if we stopped using fossil fuels immediately, there is enough carbon dioxide and other greenhouse gases stored in our oceans, which would continue to come out over the decades.

Fossil fuel burning results in more than 30 billion metric tons of CO2 being added to the atmosphere each year. With the world still dependent on fossil fuels for energy and with deforestation continuing at its current rate (cutting forests releases large amounts of carbon dioxide), we are heading towards a world that will be drastically different from the one we know today. According to Rajendra Pachauri, the Chairman of the Intergovernmental Panel on Climate Change, "every single estimate that people have come up with has been exceeded by reality…The impacts of climate change are clearly turning out to be much worse than what we had anticipated earlier." (http://www.ipcc.ch/)

The solution, of course, is to cut down on the energy we use (from fossil fuels) as soon as we can, and turn to renewable energy like wind, hydro and solar, but it is easier said than done. The oil and gas industry is very powerful and the multinational corporations are driven by greed, not altruism.

European politicians have linked the more well-known two degrees rise in temperature to 450 ppm, pointing out that any further increase in temperature will mean that we will have no chance of limiting climate change to acceptable levels. The theory is that if we can keep the amount of CO2 in the atmosphere below 450 ppm, then we might manage to keep global temperature rise below 2C. Right now, 450 ppm is more palatable to political leaders in the West and under the UN Framework Convention on Climate Change, the international community of nations has agreed that 450 ppm – linked to a rise of two degrees Celsius in global average temperatures – should not be exceeded.

So where did the 350 ppm figure come from? It originated from a NASA research team, which surveyed both real-time climate observations and emerging climatic data in January of 2008. Their peer-reviewed article concluded that above 350 ppm of carbon dioxide, the earth’s atmosphere couldn’t support “a planet similar to the one on which civilization developed and to which life on earth is adapted.”

Naturally, limiting carbon dioxide levels to 350 ppm would mean even more stringent emissions cuts, which seem unlikely given the economic recession in Europe and elsewhere.

NASA scientists like James Hansen had warned, however: “Present policies, with continued construction of coal-fired power plants without CO2 capture, suggest that decision-makers do not appreciate the gravity of the situation. We must begin to move now toward the era beyond fossil fuels. Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects”.

Some scientists now argue that we passed the safe level for greenhouse gas concentrations long ago, pointing to the accelerating impacts, from extreme weather to the meltdown of the Arctic sea ice. Others argue that we have some more room to burn fossil fuels and clear forests (but not much) before catastrophic climate change becomes inescapable. At any rate, limiting CO2 levels to 450 ppm by the end of this century will require emission cuts of 80 per cent or even more in the next 40 years. However, the current UN climate change talks are in a deadlock and no global agreement to reduce emissions is expected to be reached until 2015.

The last time CO2 levels at Mauna Loa were this high, humans did not live there. In fact, the last time CO2 levels are thought to have been this high was more than 2.5 million years ago, an era known as the Pliocene, when the Canadian Arctic had forests instead of icy wastes. The globe’s temperature averaged about three degrees centigrade warmer, and sea levels were five metres or higher. According to Tim Lueker, an oceanographer and carbon cycle researcher with the Scripps Group, “The 400 ppm threshold is a sobering milestone, and should serve as a wake up call for all of us to support clean energy technology and reduce emissions of greenhouse gases, before it's too late for our children and grandchildren”.