Far from being another unsuccessful international meeting, as some predicted, the Cancun summit is likely to be looked back upon in years to come as a seminal moment.
The accord, reached on Saturday, endorsed the actions of countries to limit greenhouse gas emissions. However, more significantly for the long term, it accepted that preserving the global environment in its present state is probably unattainable. The focus now moves to adaptation to deal with the more volatile climate that is predicted by all the major centres of climate science for the rest of this century and beyond.
The exceptional seriousness of the warming problem was underlined most recently by an International Energy Agency (IEA) report last month on the trend of increasing global emissions of greenhouse gases. Under the Copenhagen Accord's environmental goals and pledges, emissions would rise 21 per cent above 2008 levels by 2035 alone; the emissions growth rate of China (now the world's largest emitter of greenhouse gases) will increase at an even greater rate.
The IEA indicates that the increase in global temperature in these circumstances will be at least 3.5°C. There appears little that the incremental, non-legally binding Cancun accord (which builds upon Copenhagen) will do to alter this. Indeed, opposition to the deal has centred on the fact that critics, including Bolivia, assert that it would result in a global temperature rise of more than 4°C.
In the absence of moves towards a much stronger, global and legally binding deal, the world is thus on the path of the "business as usual" scenario envisaged recently as an unlikely worst case. Therefore, the international community has to consider unprecedented changes.
What is absolutely clear is that temperature rises of a 3°C to 4°C magnitude will, most likely, pose an irreversible tipping point for continental-sized areas of changing land cover, and for ice on sea and land. As a result, millions (if not tens of millions) of people are likely to be displaced by the effects of desertification and rising sea levels, and mountain snow melt.
In this fast-moving and disturbing picture, international action must now focus on how societies can adapt to (as well as prevent) these changes. And, with this in mind, politicians and the public would do well to seriously consider planning for the monumental changes in coming decades.
Put simply, as extreme weather becomes more frequent, countries will need to develop integrated practical policies that deal both with the full range of climate change adaptation and natural disasters. This year's weather-related disasters, ranging from the brush fires in Russia to the floods in Pakistan, will only grow in frequency and we must be better prepared.
In this difficult context, how is the world responding?
First, although the Kyoto accord will not be renewed in 2012, the (weaker and non-legally binding) Cancun deal that more than 190 countries have signed up to is nonetheless an important development. Key measures include a Green Climate Fund intended to raise and disburse $100 billion (Dh367 billion) a year by 2020 to protect poor nations against climate impacts and assist them with low-carbon development; and a new adaptation committee will support countries as they establish climate protection plans.
While the Cancun accord has its weaknesses, it is much better than no deal at all. And, we must be realistic: given the massively wide range of political, economic and technical approaches to climate change policy across the world, it may be impossible to frame a much stronger international agreement that would satisfy all governments, businesses and civil society groups.
The second key trend is the development across the world of a wide diversity of approaches to tackling climate change at the local, regional and national levels. In a symposium in Mexico City, organised by Global Legislators for a Balanced Environment (Globe), I heard earlier this month how collaboration in such "bottom up" initiatives will be an essential part of the global effort to tackle the dangers of climate change, and should be part of the Cancun accord.
For instance, in China, where a feasibility study is being concluded right now into a new comprehensive climate change law, financial rewards for reducing energy use provided by regional government are making substantial improvements in efficiency. These arrangements are evolving into local carbon markets, albeit small-scale and voluntary at this stage.
EU countries have been emphasising different kinds of low-carbon energy, such as wind, carbon sequestration and nuclear power. The continent has also promoted its policy of carbon trading to motivate industrial efficiency.
Other countries are focusing on preventing the rise of atmospheric greenhouse gases by expanding forestry. For instance, Brazil and Mexico are introducing national legislation for minimising the loss of tropical rain forest and preserving these irreplaceable natural habitats, while ensuring the vitality of communities who live in them.
However, despite these initiatives, we are now at a point at which preserving our current environment is probably unobtainable. What is thus urgently needed is broader agreement on a range of practical actions to mitigate climate change and deal with its effects on health, business, agriculture and natural disasters.
The rising costs of dealing with these effects, such as coastal defences, reducing desertification and urban overheating, mean that preventative actions have to begin right away. It would be folly of the highest order to delay this process until economies grow further, as some influential economists continue to argue.
Lord Hunt is a visiting professor at Delft University, the vice-president of Globe, and the former director general of the UK Met Office