On Thursday, two observatories in Hawaii confirmed that atmospheric carbon dioxide had exceeded 400 parts per million. When carbon dioxide levels were last this high, three million years ago, the world was 3 degrees hotter, the sea was at least 10 metres higher than today and camels roamed the high Arctic.
In itself, this is an arbitrary, but notable landmark in the steady rise of greenhouse gases. Before the Industrial Revolution, carbon dioxide was only 280 parts per million - since then global temperatures have risen by 0.8 degrees, with two thirds of that increase since 1975.
Yet despite great advances by low-carbon energy over the past decade, global action against climate change is still painfully slow and uncoordinated. Major - perhaps abrupt and unpredictable - changes in climate are already on the way.
The Arabian Gulf countries are in a special position. Their wealth is founded on exports of oil and gas, and on high-carbon industries and lifestyles. They may feel their money and access to technology allows them to avoid the worst consequences of climate change. But their well-being is fragile - reliant on international trade links, air conditioning, desalinated water and imports of food.
Climate change could cause or exacerbate insecurity in the Gulf's neighbours. States such as Egypt, the Sudans, Somalia, Lebanon, Syria, Jordan, Iraq, Yemen and Pakistan are exposed to a variety of ills: energy shortages, drought, land degradation, lack of water, rising sea levels, economic crises and political instability. These countries between them have 400 million inhabitants, against the GCC's 45 million. The Gulf cannot wall itself off.
But geography is not destiny. The good news is that the GCC states are also wellplaced to lead the Middle East's response to climate change. To do so, they need to rethink their economies and patterns of international cooperation.
Oil and gas will remain the bedrock of the regional economy. But, as Canada is finding out with opposition to its oil sands, high-carbon energy will increasingly face challenges- whether through widespread bans, carbon taxes or local activism.
The same applies to the Gulf's exports of petrochemicals and aluminium and to the efforts of Dubai, Abu Dhabi, Qatar and Oman to become hubs for travel, tourism and business. Expo 2020 and the Fifa World Cup 2022 will bring even more international scrutiny.
Climate action does not contradict economic growth - it supports it. Fast-rising domestic oil consumption, shortages of gas, blackouts, air pollution and depletion of aquifers already threaten the Gulf.
The GCC needs to create and commercialise technologies that address its particular needs: carbon capture and storage for gas power plants; new gas resources; dryland and saline agriculture; eco-friendly solar and nuclear desalination; ultra-efficient and solar-driven air conditioning; green architecture and urban planning for desert climates; cleaner ships and airplanes; solar panels that tolerate dust and heat.
But compared to the United States, Europe or China, the Gulf has a small talent pool.
To help to change that, the King Abdullah University for Science and Technology in Saudi Arabia, Masdar in Abu Dhabi, and the Qatar National Research Fund are investing heavily in creating the knowledge the region requires. But such institutions can be much more effective in working together on common challenges, which might also sidestep some of the political issues that hamper GCC cooperation.
By acting together, the Gulf countries could reduce their own carbon emissions, develop new technology and industries and make both themselves and their neighbours more resilient to the climate change that is now inevitable. It would be better to take action before camels again roam the Arctic.
Robin Mills is the head of consulting at Manaar Energy, and the author of The Myth of the Oil Crisis and Capturing Carbon