The day I thought would never come….global atmospheric CO2 passes 400ppm

This year the NOAA reported that the daily carbon dioxide level had exceeded 400ppm.  This is the highest concentration of this greenhouse gas in the atmosphere in at least 3 million years . It’s a day I once thought we would never see.

When I started working as a climate scientist nearly 25 years ago carbon dioxide concentrations in the atmosphere were around 350ppm. We were beginning to understand the impacts of the increase, on global warming and sea-level rise.  400ppm was discussed with policymakers as a barrier that should never be crossed, because of the risks of coastal flooding and other rapid changes that human society might struggle to adapt to.

It has been inevitable for some time that 400ppm would be breached (, but it’s a sad day now it’s here.  The hourly measurements first sneaked above this level on 17th April, the day before my birthday as it happens, and so I started my 47th year breathing air in a world with 400ppm CO2. Then on 9th May NOAA reported that the daily average measurement was 400.03ppm. The line had been crossed.

In the last 25 years, scientific research has given us a better understanding of the impacts of rising greenhouse gas concentrations.  The impacts are mainly harmful – coastal flooding, drought in some regions, biodiversity loss – but some sectors see benefits – crop productivity in some regions.  Reducing the potential harm, in as far as that is now possible, requires a long-term planning approach.  Preventing the figure rising to 450ppm requires emissions to start falling soon.  Adapting to some of the changes requires long-term infrastructure investment.  Governments are working together on this through the United Nations, and the EU, but we need to do more to avoid the dangers scientists expect.   Some people are concerned that emissions reductions in Europe will be swamped by increases in China and other emerging economies. However, the rapid and energy intensive expansion of the BRIC countries (Brazil, Russia, India and China) is slowing and moving into a technological efficiency phase (  The emissions that have led to the current high concentrations were made by USA and Europe.  China is a major manufacturer of low carbon tech. such as solar panels.

Local community and individual action is also needed. The good news is, a lot of this type of action saves money and brings other benefits.  It’s a win-win in many cases. Using less energy saves money, as well as reducing the greenhouse gas emissions caused by burning fossil fuels.  Reducing the cost of energy for heating and lighting in public buildings would reduce the running costs.  There doesn’t even have to be a cost – turning things off when they aren’t in use is free. I would rather have year-on-year lower council tax bills achieved by investment in energy saving, than a short term cut and high ongoing energy bills at leisure centres, schools and libraries.  There are lots of opportunities to reduce emissions in local authorities.  It would be wonderful to look back in another 25 years on real achievements in energy savings in Maidenhead.

The day I thought would never come….global atmospheric CO2 passes 400ppm

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