When nearly 200 countries agreed in Paris late last year to work together to reduce emissions of the greenhouse gases that cause global warming, one crucial detail was left hanging: verification.

Under the accord, the nations backed a set of principles and goals designed to stop global temperatures from rising more than 2 degrees Celsius above pre-industrial levels, the point beyond which many scientists believe catastrophic climate change will occur. Some experts questioned whether even the pact’s aspirational target of 1.5 degrees Celsius would be low enough to avoid the worst effects.

PACT BASED ON GOOD INTENTIONS

Now it turns out that the world is warming even faster than previously anticipated. NASA announced recently that last month was the warmest April on record and said it marked the seventh month in a row of global temperature records – and the third straight month that the old record was smashed by the largest margin ever. Climate experts say that 2016 will likely be the hottest year on record, by the widest margin on record. Those changes reinforce the broad scientific agreement that drastic reductions in carbon production are crucial.

The Paris accord was supposed to start us down that path, and it was an important, if late and insufficient, step forward. Yet it is an agreement based on little more than good intentions. The pact is voluntary, with international shaming of transgressors the only truncheon available. Each country is responsible for measuring and attesting to its own emissions. It is, in effect, an honor system for saving the planet.

That is a significant weakness. Beyond the obvious problem that nations can simply lie about their emissions, there’s the secondary problem of false reporting by private actors – think Volkswagen, which rigged its emissions tests for diesel engines. And there’s the possibility of simple error. Under the 1992 U.N. Framework Convention on Climate Change, industrial nations are supposed to issue annual reports on emissions, with developing countries issuing reports less frequently. But the reporting varies in reliability from country to country.

DATA MINING BY SPACE AGENCIES

A plan by a coalition of national space agencies, including NASA, could offer the kind of monitoring and verification needed to ensure that the signatory countries are living up to their word. The agencies are putting together a network of six to eight satellites that will, among other things, be able to map carbon dioxide emissions, the biggest contributor to global warming, and methane, which has more significant but shorter-term effects, from individual nations.

The monitoring idea grew out of an effort to understand “climate feedback,” such as how changes in ocean temperatures influence air temperatures, which in turn affect ocean temperatures. But scientists realized the collected data also could be mined to verify emissions.

NASA already has one satellite in place, and it will be joined in two years by a second. Japan also has put up a satellite, and others are planned by France, China and the European Space Agency. A NASA official said it was difficult to estimate what the total cost would be, but others suggest it could be in the billions of dollars.

And the science is still being developed. One trick is figuring out how to separate readings of human-caused carbon dioxide emissions from naturally occurring, uncontrollable emissions – forest fires, volcanoes and rotting vegetation, for instance. But the scientists are confident they can make it work.

And they should. Of course, such a system is contingent on government funding. Here in the United States, with climate-denying politicians both in Congress and running for president, continued support is not guaranteed. Which is yet another indicator of how crucial this fall’s election will be.