This commentary on originally appeared online at DevexThe international community has a rare opportunity in 2015 to confront two linked global challenges: extreme poverty and climate change.In September, the United Nations is expected to agree on a new agenda aimed at eradicating poverty and advancing sustainable development. In December, climate negotiators will gather in Paris, France, to reach an agreement to accelerate the shift to a low-carbon economy and strengthen resilience to climate change.Success this year will depend on whether or not we can develop a new model for international cooperation that is universal — including all countries — yet differentiated — recognizing differences between countries.Twenty years ago, the development and climate communities divided countries into two groups — rich and poor — and specified who needed to do what. Today, such a binary distinction is much less relevant given the rapidly changing economic and political context.The Solutions We NeedWhat we need are solutions that involve all countries but that respect the differing levels of responsibility and the capacity of individual countries to respond to these twin challenges.The U.N. Framework Convention on Climate Change, established in 1992, led to the Kyoto Protocol and binding targets among developed countries to curb greenhouse gas emissions. The protocol reflected the thinking of its time: It divided the world into developed countries that needed to cut carbon pollution and developing ones that did not. Economic development and emissions profiles have changed dramatically since then and an agreement that only expects cuts from developed countries will ultimately fail to prevent catastrophic warming.The story is similar for efforts to reduce poverty. The Millennium Development Goals, launched in 2001, imagined a world where developing countries could improve the lives of their poorest citizens, with developed countries providing aid and other support. While income poverty — the number of people living on $1.25 a day or less — has been significantly reduced, with impressive gains made in providing basic education and health services, there is now recognition that eradicating extreme poverty will require more than just aid and good domestic policy. It will also require a broader suite of actions from all countries — and across economic, social and environmental realms.What is the architecture we need for international cooperation in this new world? And how can we ensure that the commitments countries make, in aggregate, are sufficiently ambitious to tackle these two challenges and be sufficiently fair to ensure global engagement?We are starting to see the outlines of a new model for just this kind of international cooperation.From Top-Down to Bottom-UpThe next international climate agreement will shift from a top-down, legally binding system that specifies how much each developed country must reduce greenhouse gas emissions, to a bottom-up approach where all countries — developed and developing — determine their own level of commitment.Whether these voluntary pledges will collectively set us in the right direction to keep the world at or below 2 degrees C (3.6 degrees F) of warming above pre-industrial levels is a critical question. An equally important question is whether the pledges are perceived as fair, given that the contribution and capacity to tackle this problem varies considerably between countries.Last November’s pact between the world’s largest historic emitter, the United States, and its largest current one, China, sends a crucial message about the importance of working together, while respecting differences.The proposed sustainable development goals reflect a similarly important shift. Unlike the MDGs, these goals and their associated targets will be universal in scope. Poverty is not confined to the developing world. Developed countries are expected to adopt the agenda and take actions to eradicate poverty and achieve sustainable development within their own borders, as well as ensuring that relevant policies such as those on trade, investment or migration support developing countries in tackling poverty. Finally, all countries will be expected to tackle global challenges, such as climate change, that threaten to exacerbate poverty if left unaddressed.2015 will not answer all questions related to these twin challenges, but it will lay the framework for international cooperation for the next decade. The emerging architecture will require all countries to work together. If designed well, it can set the stage for true transformation that can benefit the hundreds of millions of people still struggling to escape poverty, as well as those facing the mounting threats of climate change. The stakes are high. We have a once-in-a-generation opportunity to get this right.