There are a few notable absentees among the more than 120 world leaders gathered in New York for yesterday's United Nations Climate Summit.
Perhaps most notable of all is the head of the world's highest-emitting nation, China's President Xi Jinping.
Others who could make a difference have also sent their apologies, including Indian Prime Minister Narendra Modi, Russian President Vladimir Putin, Canadian Prime Minister Stephen Harper, and Australian Prime Minister Tony Abbott.
India and Russia are the third- and fourth-largest emitters, respectively, whereas Canada and Australia have some of the world's highest per capita emissions.
The roll-call of absentees might signal a loss of political confidence in international climate policies, notably those established through UN negotiations.
But that is not to say that the biggest polluters are doing nothing.
In President Xi's case, it is tempting to conclude that he and his country are forging ahead without waiting for international agreement.
Outside the meeting and across the world, street protests have loudly called for greater efforts by major countries.
Leaders who are not attending the summit have received criticism, even if they have sent senior figures to represent them.
The 2014 meeting is the largest gathering of leaders for UN climate talks since the 2009 Copenhagen conference, which resulted in only a weak political statement and no legally binding commitments to reduce emissions.
The Copenhagen conference featured former Chinese premier Wen Jiabao, as well as former Indian prime minister Manmohan Singh.
This year, the Chinese delegation is led by Vice-Premier Zhang Gaoli, a less senior figure than President Xi, and than Mr Wen Jiabao's successor, Premier Li Keqiang.
China is the world's largest producer of carbon dioxide emissions (in absolute, rather than per capita, terms). Hence, it is a big contributor to the greenhouse problem.
But it is also emerging as a world leader in solutions to it.
Besides leading the world in renewable energy investment, China now hosts the world's second-largest carbon trading network, which deals in emissions permits equivalent to 1.1 billion tonnes of carbon dioxide each year, spread across several pilot schemes in designated cities and provinces.
China has recently unveiled plans for a national carbon price that would dwarf the European Union's Emissions Trading Scheme by the end of the decade.
In the meantime, China's existing regional carbon markets, while continuing to reduce domestic emissions, could also form a template for similar regional schemes around the world.
The absence of China's most powerful person from the United Nations summit should not be taken as evidence that China does not want to act on climate change.
In fact, China's recent domestic commitments in emission reduction - including carbon intensity reduction, emissions trading, and low-carbon city initiatives - are quite aggressive, given that its economy is still developing.
Rather, it might reflect a loss of political confidence in international climate policy, the most notable example of which is the UN's Kyoto Protocol.
China participated in the protocol's Clean Development Mechanism (CDM), which aimed to deliver emissions reductions by trading carbon credits around the world.