It took less than 140 characters for Hillary Clinton to make a convincing case to her environmental critics that she's committed to keeping carbon underground and protecting some of America's most unique, sensitive habitats.

The Arctic is a unique treasure. Given what we know, it's not worth the risk of drilling. -H — Hillary Clinton (@HillaryClinton) August 18, 2015

Clinton’s position against drilling in the Arctic is a clear break from the Obama administration, which gave Shell final permission on Monday to explore for oil in the Chukchi Sea of Alaska through late September.

The environmental group 350 Action, among Clinton’s harshest critics on climate issues, offered rare praise Tuesday for Clinton’s leadership—while noting she still hasn't taken a concrete position on the group’s top target, the Keystone XL pipeline.

"This is a hugely encouraging sign from Hillary Clinton, and it's in no small part thanks to activists in Seattle, Portland, and around the country who've placed their bodies on the line to put Arctic drilling and the broader issue of climate change on the political map,” 350 Action spokesperson Karthik Ganapathy emailed the New Republic. “It's not easy to stand up to Big Oil, nor to break with a sitting President from within your party—so Secretary Clinton deserves real credit for that."

In some ways, a candidate's position on Arctic drilling is more consequential than the Keystone XL pipeline. President Barack Obama's final decision on the proposed pipeline is expected to come soon, whereas the next president will set the agenda for offshore drilling, including in the Arctic. According to federal estimates, the U.S. Arctic contains 30 billion barrels of undiscovered oil: the equivalent of running the Keystone XL pipeline at full capacity for 75 years, even if you count the added carbon emissions from tar sands oil, according to Natural Resources Defense Council Arctic Director Neil Lawrence. If Keystone is ever built, the State Department has put the pipeline’s lifespan at roughly 50 years.