Former Vice President Joseph R. Biden Jr. announced his environmental plan this week, and it shows how far the Democratic field is moving on climate change.

Under the proposal, the United States would aim to be carbon neutral by 2050, in part by putting a price tag on planet-warming pollution. The plan also calls for public investments of $1.7 trillion in clean energy and other environmental initiatives over 10 years.

Just last month, Mr. Biden’s rivals were accusing him of being weak on climate change.

“This definitely goes further than the Obama administration in terms of aspiration,” said Robert N. Stavins, an environmental economist at the John F. Kennedy School of Government at Harvard University. “This clearly demonstrates that Biden and his people recognize the polling that Democrats in the primary electorate are skewed to the left, and the polling demonstrates that they care about climate change.”