As the world hails the success in reaching an agreement at the recently concluded climate change summit in Paris ("Historic climate change deal may signal end of fossil fuel era"; Dec 14), there is reason to be cautious.

While the agreement does indicate that nations should try to keep the rise in global temperatures to 2 deg C or even 1.5 deg C above temperatures before the industrial revolution, the current national commitments by all nations (known as INDCs) fall far below this mark.

An important point to keep in mind is that in March, the world passed 400 parts per million (ppm) of carbon dioxide into the atmosphere, which is 50ppm above what is believed to be a safe limit to prevent disastrous climate change.

The last time the world had this much carbon dioxide in the atmosphere was between 2.6 million and 5.3 million years ago.

As a result, the world is already almost 1 deg C warmer, which is just 0.5 deg C from the lower temperature limit in the agreement.

The potential effects may be the reason why 10 of the past 12 years have been the hottest since records began 135 years ago.

The agreement is a pragmatic beginning. Climate action cannot be imposed on people or nations.

To this end, the agreement requires INDCs to be reviewed every five years, which gives flexibility for nations to change their commitments over time.

It allows for the crucial element that national actions on climate change will change as technology and, crucially, society's attitudes evolve.

There is clearly reason to be optimistic that effective climate action is possible, but this may depend more on the attitudes of society as a whole rather than agreements alone.

Lahiru S. Wijedasa