[Editor's note: This article was authored by BSR, a global business network and consultancy focused on sustainability.]

Last month's release of the Global 500 Report, Carbon Disclosure Project's (CDP) annual summary of climate reporting by the world's 500 largest companies, gives the most insight to date on corporations' reporting about climate change and their supply chains.

What does it tell us?

First, the number of companies reporting on their supply chains continues to steadily grow. Two years ago, only about a quarter of the world's top 500 companies reported on "Scope 3" greenhouse gas (GHG) emissions, or the emissions from activities they have influence over, but are beyond direct ownership or control, such as in supply chains.

Last year, the reporting share climbed to 42 percent, and this year it grew to nearly half. That's a steep change compared to reporting overall, which rose only a few percentage points this year to 82 percent.

At the same time, the quality and scope of reporting is improving dramatically. This year, for example, Kraft Foods said physical risks linked to climate change are not material, but they still described a whole set of supply chain and other issues that potentially matter. Kraft also clarified that they are closely examining supply chain issues to anticipate emerging enterprise risk and opportunities. The provision of this depth of information is a new development in CDP reporting, and has been aided in part by the more systematic ways that CDP is asking questions.

This relates to a third development: CDP made Scope 3 reporting more robust by expanding definitions this year. In following the Greenhouse Gas (GHG) Protocol's Scope 3 Guidance under development, CDP transformed last year's five categories into eight more specific ones, and then added nine more (see sidebar).

This helps transparency by increasing the comparability of reported figures. It also foreshadows the increasing sophistication of supply chain reporting to come. Indeed, Frances Way, CDP's Head of Supply Chain, told me that CDP will continue working to ensure reporting requirements are aligned with the standard once finalized. Meanwhile, CDP is taking public comments on the design of the next survey.

Scope 3 emissions have taken center stage and turned out to be every bit as significant as we thought they would be. This raises an important question: Just how big are they?

In the summary report, CDP tallied aggregate figures by industry, finding Scope 3 to be on average about two times the amount of Scopes 1 and 2 emissions, which are sometimes called "internal" emissions. It will take a little digging, however, to get a representative number since 50 percent of companies don't report Scope 3 at all. Of those that do, 40 percent only publish just one convenient category, such as transportation.

The companies to watch are the 10 percent that reported supplier emissions, and the even smaller 5 percent that reported supplier emissions beyond direct purchasing relationships.