(Bloomberg) -- President Joe Biden pledged to halve U.S. greenhouse gas emissions by 2030 and increase financial aid for developing countries that curb their pollution, as he convened 40 world leaders in a virtual summit intended to demonstrate renewed American resolve to fight climate change.Biden announced in opening remarks for the two-day summit that the U.S. will reduce its own greenhouse gas emissions 50%-52% from 2005 levels by the end of the decade -- significantly boosting a commitment made under former President Barack Obama that was scrapped by former President Donald Trump.“No nation can solve this crisis on our own,” Biden said Thursday from the White House. “All of us, and particularly those of us who represent the world’s largest economies, we have to step up.”He later said that the U.S. would double annual foreign aid to developing countries fighting climate change. His initial fiscal 2022 budget request submitted to Congress earlier this month included $2.5 billion for climate aid.The new U.S. pledge to curb emissions is aimed at encouraging industrializing countries including China, India and Brazil that account for much of the world’s carbon output to set their own aggressive emissions-reductions targets. But Biden faced a cool reception from leaders worried about committing to emissions cuts that could slow economic growth.In their opening statements, the leaders of China and India kept to previously announced targets, and Brazil’s Jair Bolsonaro explicitly tied his country’s efforts -- including a pledge to curb deforestation -- to financial assistance from wealthier nations.Biden must also confront overseas skeptics who have watched U.S. climate policy shift dramatically depending on the occupant of the White House and wonder whether the latest U.S. president’s promises can be trusted.Biden’s pledge would require changes that would touch the lives of nearly every American. But Republicans in Congress are unlikely to support legislation that would make major reductions in U.S. emissions, for example by penalizing fossil fuel use or mandating renewable power, and any regulations Biden’s administration issues are sure to face challenges from industry.“Scientists tell us that this is the decisive decade,” Biden said at the summit. “This is the decade we must make decisions that will avoid the worst consequences of the climate crisis. We must try to keep the earth’s temperature to an increase of 1.5 degrees Celsius.”All 40 of the leaders invited, from British Prime Minister Boris Johnson to Chinese President Xi Jinping and Russian President Vladimir Putin, agreed to attend and speak. Other participants include Pope Francis, members of indigenous groups from around the world, and current and former corporate executives including Bill Gates and Michael Bloomberg, founder and majority owner of Bloomberg News parent company Bloomberg LP.“We are at the verge of the abyss,” UN General Secretary-General Antonio Guterres said after Biden, describing the planet as “racing” toward a 1.5-degree increase in average temperatures.Xi described environmental protection in terms of productivity.“To protect the environment is to protect productivity, and to improve the environment is to boost productivity,” he said. “We need to make sure that a sound environment is there to buttress sustainable economic and social development worldwide.”Bolsonaro said his country is committed to eliminating illegal deforestation by 2030, allowing a reduction in carbon dioxide emission. Deforestation has been a persistent problem in the Brazilian Amazon.But Bolsonaro cautioned that “there must be fair payment for the environmental services provided by our biomes to the planet at large as a way to recognize the economic nature of environmental conservation activities.”Australian Prime Minister Scott Morrison sidestepped his country’s role as a major coal producer and focused instead on its efforts to produce new technologies to fight climate change. He announced $1.5 billion in climate financing focusing on the Pacific region.The gathering is aimed at driving more aggressive climate action that may keep average global temperatures from rising more than 1.5 degrees Celsius (2.7 degrees Fahrenheit), a key tipping point.Comparing countries’ varying commitments to cut emissions is nearly impossible because there is no international agreement on calculating the figures. To reach accord in the Paris agreement, for example, countries were allowed to each set voluntary goals, choosing their own baselines and end-dates, without coordination.Biden’s target is intended to put the U.S. on track to reach net-zero emissions by 2050. Biden has frequently highlighted that goal -- a point where the greenhouse gases added to the atmosphere by the U.S. are completely offset by reductions.The 50%-52% pledge was based on an analysis of the potential for different sectors of the economy to pare greenhouse gases, according to administration officials. The Biden administration opted not to make an explicit commitment to pare emissions of methane as part of the pledge, despite entreaties from environmentalists.Pledges of AlliesSome U.S. allies announced plans to boost previous pledges.Canadian Prime Minister Justin Trudeau raised his nation’s target for greenhouse gas reductions to 40% to 45% by 2030, “blowing past” a previous goal of a 30% reduction from 2005 levels. Japanese Prime Minister Yoshihide Suga raised his country’s target to a 46% reduction by 2030 from 26% previously.China reiterated previous plans to peak carbon emissions by 2030 and to attain net-zero status by 2060. While that wasn’t new, Xi also pledged to reduce coal consumption between 2026 and 2030.Ahead of the summit, former Secretary of State John Kerry, Biden’s special presidential envoy for climate, offered some praise for Beijing’s plans.“Obviously we have differences with China on certain issues, and climate has to be treated separately,” Kerry said, referring to rifts on trade and human rights, among other issues. “They didn’t just talk about plateauing or peaking, they have now agreed there must be actions between 2020 and 2030.”Biden’s climate pledge is less ambitious than the European Union’s target of reducing its emissions 55% from 1990 levels by 2030, and it falls below a coming U.K. goal to achieve a 78% reduction by 2035 from 1990 levels. A 50% cut from 2005 emissions would amount to just a 40% cut for the U.S. when recalibrated to the same 1990 baseline.The current goals laid out by China and India are not aggressive enough to keep global temperature increase below 2 degrees Celsius, according to BloombergNEF.Russia’s Putin reiterated a goal he announced in his annual state-of-the-nation address on Wednesday: that the cumulative volume of the country’s net emissions should be less than those of the European Union over the next three decades. Analysts are skeptical Putin’s goal will amount to a real policy change, noting Russia’s emphasis on continuing to extract fossil fuels from the Arctic.“It is no secret that the conditions that facilitated global warming and associated problems go way back,” Putin said at the summit. “Carbon dioxide can stay in the atmosphere for hundreds of years. So it’s not enough to tackle the issue of new emissions. It is also important to take up the task of absorbing the CO2 that has accumulated in the atmosphere.”Russia, he stressed, “makes a gigantic contribution to absorbing global emissions, both ours and from elsewhere.”But none of the pledges by any nation are binding, and meeting the most ambitious targets will require dramatic changes in the way the world generates and uses energy. It would also require emissions reductions from hard-to-decarbonize sectors of the economy, from cement-making to agriculture.“Targets, on their own, won’t lead to emissions cuts,” said Kate Blagojevic, the head of climate issues for Greenpeace UK. “That takes real policy and money. And that’s where the whole world is still way off course.”Environmentalists argue Biden’s planned emissions reduction is both achievable and ambitious -- a sweet spot essential to U.S. credibility. However, fulfilling the commitment still depends on a slew of yet-to-be-written environmental regulations that can be ripped up by future presidents, Biden’s multitrillion-dollar infrastructure package that faces stiff opposition in Congress and a rapid transformation of the U.S. electrical sector.U.S. Political DisputesBiden’s efforts come after Trump pulled the U.S. back from the climate fight. He withdrew from the Paris Agreement on climate and his administration systematically dialed back Obama-era climate policies, including efficiency standards to curb electricity use and rules cutting greenhouse gas emissions from power plants, automobiles and oil wells.Yet Biden also faces concerns within his own domestic political base as he tries to navigate competing pressures from Senator Joe Manchin, a Democrat from coal-rich West Virginia, and progressives such as Representative Alexandria Ocasio-Cortez and the Sunrise Movement.On the eve of the summit, Sunrise’s political director, Evan Weber, took a swipe at Biden’s planned emissions cut, arguing that a 50% reduction falls far short of what the U.S. needs to do as “the richest country in the world and the biggest historical polluter.”“The science is clear – if the U.S. does not achieve much, much more by the end of this decade, it will be a death sentence for our generation and the billions of people at the front lines of the climate crisis in the U.S. and abroad,” Weber said in a statement.The Biden administration is building its target on a foundation of domestic climate programs and policies, including investments in renewable power and electric vehicles as well as regulations throttling greenhouse gas emissions from power plants, oil wells and automobiles.Still, there are technical and economic barriers. To meet its commitment, the U.S. would need to curtail emissions from across all reaches of its economy, including the energy, transportation and industrial sectors. The country would have to rapidly scale up renewable power, shift more of the nation’s vehicles to zero-emitting electric varieties and quickly deploy carbon-capture technology at manufacturing facilities.Oil industry advocates, including Republicans on Capitol Hill, have already panned Biden’s expected pledge as too aggressive, with Senator John Barrasso, a Republican from Wyoming, describing it as a “punishing” target that “will cost working families a fortune in higher energy bills” while harming America’s competitiveness.(Updates with additional Biden remarks in fourth paragraph.)For more articles like this, please visit us at bloomberg.comSubscribe now to stay ahead with the most trusted business news source.©2021 Bloomberg L.P.