This year marks the five year anniversary of the C40 – CDP partnership.  In 2010, then Mayor of New York and C40 Chair-elect Michael Bloomberg announced the beginning of our partnership at a C40 workshop in Hong Kong. “We will never meet the ambitious goals we set as an organization without solid data to measure our progress,” Bloomberg noted. “As I've always said: if you can't measure it, you can't manage it."

From that day, the CDP – C40 relationship has been about a radical commitment to transparency and accountability—enabled by data.  Nowhere is this commitment clearer than in our joint approach to annual reporting.  Every year since 2011, CDP and C40 have invited the member cities of the C40 to report their latest climate change data through CDP’s system – and nearly all cities now participate. This data is now more accessible than ever with the recent launch of CDP’s open data portal.

CDP’s open data portal enables users to view, download, and interact with CDP’s full database of self-disclosed climate change data from C40 cities, covering areas like greenhouse gas measurement and reporting, identifying climate risk, and setting emissions reduction targets. Some 61 C40 cities, representing 21% of global GDP, report new data every year.

When looked at in its entirety, this data reveals some exciting trends. Over the past 5 years the number of reporting cities has grown by nearly 50 percent. It also shows that over 67% of cities are reporting their GHG emissions and 53% view climate change as a serious and near-term risk to their city.

As an example of how to utilize this data, let’s look first at GHG measurement and reporting among C40 cities.  C40 cities around the world measure and report their total greenhouse gas emissions every year.  The map below shows total emissions from each reporting city, as well as additional information about their emissions inventory: the measurement year, what protocol they used, and a description of why emissions rose or fell against last year’s total. 

We can also examine in depth the climate risks that cities face.  In 2014, C40 cities reported more than 250 individual climate risks, including more intense heat waves, hotter summers, and increasing frequency of droughts.  New York City, for example, expects that the frequency of large storms like Hurricane Sandy will increase over the medium-term.  “The annual chance of a storm overtopping the seawall has gone from about 1 percent to 20 to 25 percent,” reports the city government. The chart below shows the most common climate risks reported by C40 cities in 2014. 

These are but a couple of examples of the way C40 and CDP’s commitment to transparency through open data enables greater understanding of the way cities are measuring, monitoring and managing their impact on the environment, and the climate risks they face.

Transparency and accountability are more important than ever this year, as nations convene around a new climate agreement in Paris in December. CDP’s open data portal is in step with a larger movement among cities now joining the Compact of Mayors, the largest coalition of city leaders publicly reporting climate targets, inventories and plans. Through their commitment, cities will help nations set and achieve more ambitious climate targets, and will contribute to a global climate solution.


You can view more climate change-related data from C40 cities at — and the full set of open data, including emissions reduction targets for every city—at

To learn more about the Compact of Mayors, click here.




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