Andrew reports that the biggest hurdle for President Biden in winning new emissions reduction commitments at this week's White House summit is America's on-again, off-again history of climate change efforts.

Why it matters: The global community is off-course to meet the temperature targets in the Paris climate deal. The White House wants the summit Thursday and Friday to begin to change that.

• The Paris Agreement called for warming to be limited to "well below 2 degrees" Celsius, or 3.6 degrees Fahrenheit, relative to preindustrial levels.
• But the world is currently on course for 3 degrees Celsius, or 5.4 degrees Fahrenheit, of warming, which raises the odds of potentially disastrous consequences.

The big picture: The U.S. has been playing "red light, green light" on climate for decades. The country played a leading role in brokering the Kyoto Protocol in 1995 but walked away in 2001.

• Then the U.S. helped spearhead talks on the Paris Agreement during Barack Obama's presidency, only to leave that agreement under Donald Trump and rejoin when Biden took office.
• Now other countries — including China, the world's top emitter by far — question the Biden administration's word when it says the U.S. is fully committed to action.
• For example, on Friday Chinese Foreign Ministry spokesman Zhao Lijian said of the U.S. return to Paris: "Its return is by no means a glorious comeback but rather the student playing truant getting back to class."

Quick take: "The way to rebuild the trust is for this Administration to first explain how the United States will achieve its Paris target and then also provide a concrete plan for enhancing ambition by 2030," said Kelly Sims Gallagher, a Tufts University professor who helped broker a climate deal with China during the Obama administration.

Context: The White House summit will test how much credibility the U.S. lost on the global stage after Trump walked away from Paris and worked to gut domestic efforts to cut emissions.

The intrigue: The joint communique released by the U.S. and China Saturday night indicates there may be a window for progress between the world's top two emitters despite major tensions.

The state of play: The Biden administration wants countries to agree this week to cut emissions significantly by 2030, on the way to net zero by 2050.

• The U.S. is expected to unveil an emissions reduction commitment on the order of a 50% emissions cut relative to 2005 levels by 2030, but it's unclear how many other nations will announce anything new ahead of November's United Nations climate talks in Glasgow.

Yes, but: Even if the White House and U.N. talks are successful, it's unknown whether new emissions targets will actually be met, considering the lack of an enforcement mechanism to punish countries that don't live up to their word.

Read more.

The odds of calamitous climate events, from collapsing polar ice sheets and the ensuing sharp rises in sea levels to deadly heat waves, increases dramatically if the world exceeds the Paris Agreement's temperature targets, Andrew reports.

Why it matters: In order to have a decent chance of meeting the agreement's most ambitious temperature target — holding warming to 1.5 °C above preindustrial levels — greenhouse gas emissions need to be sharply reduced before 2030.

The big picture: With the world hurtling toward potentially catastrophic levels of warming, a Herculean effort involving a slew of clean energy technologies is needed to pivot to a different emissions path.

How it works: If the world waits until the 2030s to bend the emissions curve downward, the pace of cuts required to meet the agreement's temperature targets would likely be too expensive, and may be technologically impossible.

What they're saying: John Kerry, Biden's climate envoy, told reporters Saturday that committing to reach net-zero emissions in 2050 is insufficient.

• "Many people are focusing on 2050 net this, and 2060 net that. That’s good, and we’re happy to have people do it, but not to the exclusion of being super-focused on this decade," Kerry said in Seoul.
• "If we don’t do what we need to do between 2020 and 2030, those other things become impossible."

Get ready for lofty statements, urgent calls for carbon-cutting progress, new pledges — and known unknowns about how much concrete action will follow, Ben reports.

What we're watching: The White House will showcase a new 2030 U.S. emissions-cutting target at President Biden's global climate summit this week.

• And Bloomberg reports the administration is slated to unveil plans for billions of dollars to help developing nations fight climate change.
• A White House executive order aimed at bolstering U.S. policies on climate-related financial risk could also emerge this week.
• Outside the U.S., some countries that haven't yet disclosed revised Paris targets may do it this week (lots of eyes are on Japan) and make other commitments.

Reality check: Emissions targets are simply aspirations, even if they provide some impetus for concrete new policies.

Meanwhile, various companies will unveil new sustainability pledges around the summit and Earth Day, which is Thursday.

• It's already starting. Scroll down for some Amazon news.
• The Wall Street Journal reports BP is vowing to largely end burning of natural gas that's a byproduct of Permian Basin oil wells.
• The company plans to spend $1.3 billion on infrastructure to enable the changes, it reports.

Cities and states continue to push forward on their climate goals, raising their level of ambition, Andrew reports.

Why it matters: Cities account for a significant share of emissions and worked to reduce them despite the Trump-era federal pullback. City leaders also must prepare for climate impacts such as the sea-level rise and more intense heat waves.

Driving the news: On Friday, 96 more cities committed to halving their emissions by 50% by 2030, while aiming toward net zero by 2050, per C40 Cities, a network of the world’s megacities committed to addressing climate change.

This brings the total to 125 mayors from 31 countries, including the leaders of Bangkok, Mumbai, Rabat and Miami Beach.

By the numbers: Antha N. Williams, head of the environment program for Bloomberg Philanthropies, told Axios that local action helps provide the U.S. with gravitas on climate despite federal inaction.

• "U.S. credibility on climate rests with the fact that local leaders have been delivering on climate action," she said.

Yes, but: While any city emissions cuts are helpful, they can only partially address some of the largest emissions sources nationally and internationally, such as transportation and electricity.

• There are also questions about how much emissions reductions at the local level would have happened anyway with more cost-competitive renewables and other developments, absent the work of C40 and other initiatives.

International Energy Agency modeling underscores the kind of sweeping energy transformations needed in the relatively near future to meet the Paris goals, Ben reports.

The big picture: The chart above via IEA's World Energy Outlook last October shows changes in demand for various fuel sources in three IEA scenarios.

• The first shows its estimates under nations' current and announced policies at the time, which bring warming well in excess of the targets.
• The second two are pathways for keeping the very ambitious 1.5 °C target in sight to varying degrees by reaching net-zero emissions in 3-5 decades (but it's complicated and you can read more about them here).

Why it matters: Keeping the Paris targets in sight requires huge changes this decade. The chart above shows greatly accelerated renewables deployment, a steep drop in coal use and other big shifts.

• IEA's hardly alone in the long-term scenario business and any multidecade look-ahead is stuffed with uncertainties.
• But what's common among scenarios for holding warming significantly in check is a rapid shift away from fossil fuels.

Amazon this morning announced investments in several new utility-scale wind and solar projects and said it's now Europe's largest corporate renewable power buyer, Ben reports.

The big picture: Look for a burst of corporate clean energy and climate pledges this week as companies hope to show their bona fides alongside the White House event and Earth Day.

Driving the news: Amazon said it is investing in nine new projects in North America and Europe.

• They include a California project that Amazon's first solar development paired with battery storage. Others include a U.K. offshore wind project and new projects in Spain and Sweden.
• Amazon said the new developments bring its global renewables portfolio to 206 projects with a generating capacity of 8.5 gigawatts — including 2.5 GW in Europe it calls enough to power over 2 million homes annually.

Why it matters: Companies' renewables procurement is now an important driver of wind and solar development. The tech industry overall has been the largest buyer.

The intrigue: Companies are using the political spotlight on global warming to tout their clean-tech investments and climate pledges.

• But environmentalists say expanded corporate efforts are not enough — they want Big Tech to stop providing sophisticated computing services tailored to oil companies.
• JPMorgan Chase and Citigroup last week expanded their sustainable financing pledges through 2030, but activists highlighted their continued work with fossil clients.