Yesterday India and China notified the United Nations that they would join the climate deal created at December's climate conference in Copenhagen, Denmark.

(Relive the fun with OnEarth's Copenhagen Climate Talks coverage.)

The Associated Press reports that "[A] one-sentence note from China's top climate change negotiator, Su Wei, authorized the addition of China to the list attached to the nonbinding accord brokered by President Barack Obama in the final hours of the December climate change summit in the Danish capital.

"India sent a note on Monday that it 'stands by the contents of the accord.'"

Among the world's top greenhouse gas polluters, with fast-growing industrial and consumer economies, it was crucial that China and India accept the Copenhagen pact. 
They're the last of the world's major economies to become parties to the accord, joining around 100 other nations in accepting the deal.  

The legally-toothless agreement pledges to keep global mean temperature increases from pre-industrial levels at or below 3.6 degrees Fahrenheit (2 degrees Celsius).

The pact also commits the world's richest industrial nations to providing $100-odd billion in climate-change-related aid to poorer developing nations. The funding would go to helping these countries leapfrog into low-carbon economic development, as well as adapt to changing climate and weather conditions. 

For all that they're good news, China and India's moves don't yet answer the biggest open questions in international climate politics: 

It remains to be seen whether broad international buy-in to the Copenhagen Accord will get major emitters to aim for the targets they defined for cutting heat-trapping greenhouse gas pollution.  Or whether they'll allow transparent, international monitoring of their reduction and mitigation efforts, a key demand of developing nations by the Obama administration. 

It's also hard to gauge what impact this will have on the chances of creating a legally binding agreement at November's international climate talks in Mexico.

But China and India's participation in Copenhagen may weaken one argument by climate-challenged senators: that the US would be taking an economic hit if it cut emissions while these two up-and-coming economic powerhouses stood off to the side.

That in turn could undergird efforts by the Obama administration, as well supportive lawmakers, to get decent climate and energy policy reform through the Senate.  

The first commitment period for cutting greenhouse gas pollution under 1997's Kyoto Accord ends in 2012. Without establishing new targets, as well as internationally-accepted means and measures for meeting them, both governments and industries will find it hard to plan effective responses to climate change.

Which is more or less another way of saying that they'll find it even easier to put off taking politically controversial actions to re-stabilize the climate, as well as potentially far-reaching and costly steps to adapt to the changes already under way.

Also read: India Increases National Action on Climate Change, on NRDC's advocacy blog Switchboard

Video: The Daily Show, Wednesday February 10, 2010: "Unusually Large Snowstorm -- Aasif Mandvi freezes in New York, Sam Bee feels the heat in Australia, and Jason Jones reports on the darkness everywhere."