22/09/2014 06:41 BST | Updated 19/11/2014 05:59 GMT

Our Last Chance To Curb Greenhouse Gas Emissions

As world leaders gather in New York for the UN Climate Summit, intended to galvanise global climate action, they do so on the cusp of a once-in-a-generation opportunity to prevent warming going over 2˚C above pre-industrial temperatures. This is the key message in the annual Global Carbon Budget, published today.

The findings are stark.

In 2014, CO2 emissions from fossil fuels and deforestation will reach 40 billion tonnes, the highest annual emissions in human history.

About two thirds of the total CO2 emissions quota available for human activity to still have a fair chance of limiting warming to under 2˚C, has been used up. A 2˚C warmer world will pose challenges for most countries, developed and undeveloped. The 2009 Copenhagen climate talks set a target of limiting warming to under 2 ˚C, but how feasible this will be remains to be seen.

If CO2 emissions continue at 2014 rates, the remaining third of the quota will be used up within a generation. To have a fair chance of achieving the 2˚C target, much of the known reserves of fossil fuels need to remain in the ground and unexploited. Without rapid emissions reductions at a global level, children born today could live in a world that has used up its CO2 emissions quota by the time they reach adulthood.

Emissions are expected to grow further over coming years, particularly in rapidly-growing economies

In 2013, China, the United States, the European Union and India together accounted for 58% of global emissions. China's per capita emissions outstripped Europe's for the first time. Emissions in the USA increased 2.9% following a rebound in coal consumption, reversing the declining trend in emissions since 2008. It's projected they'll remain at this level for at least the next five years. Emissions in the European Union decreased 1.8%, on the back of a weak economy, but the long-term decrease in EU emissions masks a significant amount of emissions which are 'exported' through goods and services, produced elsewhere for consumption within the EU. When these emissions are accounted for, EU emissions have stabilised.

To stop the world warming over 2˚C with a 50% chance of success, average global rates of emissions must reduce by roughly 5% per year.

These rates of change are completely unprecedented - global rates of improvement due to efficiency gains are typically in the range 1-2% per year, for instance. Reducing emissions at such a rapid rate would require reversing the upward trend in global CO2 emissions, and decoupling GDP growth from growth in emissions. A possible technological 'fix' that would secure negative emissions later in the 21st century by removing carbon dioxide from the atmosphere has been suggested, but at present options are limited. Bioenergy with carbon capture and storage could provide enough negative emissions to cope with mitigation requirements, but there are still uncertainties over its environmental and social implications, as well as its economic feasibility.

The remaining CO2 emissions quota will be 'shared' amongst nations, by design or by default.

The Global Carbon Atlas invites visitors to the website to make country-by-country comparisons. It allows us to compare the consistency of a country's local actions in the context of the global goal. We can also ask the question 'if we act consistently according to our proposed share of the global quota, would that be achievable and acceptable to us?' Policymakers, business and consumers face hard choices.

Keeping planet Earth from warming to 2˚C is the great challenge for our generation.

Scientists and society have succeeded in reaching the South Pole, putting a man on the moon, and mapping the human genome. Reducing CO2 is a different kind of challenge, one which will not be met by one nation or individual, and which will require technological, economic, social, political and behavioural changes. We also know that 2˚C already implies serious new economic, social and ecological risks.

It is essential that the political negotiations now beginning in earnest in the run-up to the 2015 climate conference in Paris are informed by the best scientific evidence, and a better understanding of development pathways that can secure equitable and sustainable transformations of energy and land-use. This requires contributions from a new type of science that links disciplines, knowledge systems and partners from civil society to support a more agile global innovation system. We need to open up knowledge, putting information in the hands of the decision-makers, researchers, and anyone who wants to use it.

The people's climate marches that took place yesterday - I joined the march in New York - explain the concept of a new contract between science and society better than any of the reams of documentation produced to make the case for action on climate. It is time to turn that citizen energy into action.