Dear President Obama,

As the lead negotiator for the world's 48 Least Developed Countries (LDCs) in the United Nations climate change negotiations, I congratulate you on your re-election. I also want to express my admiration for your response to superstorm Sandy: without the preparations that you made, the impacts to those hit by the storm would have been even more devastating. As communities in the north-east work to rebuild and recover, the world has an opportunity to begin a new, reality-based conversation about climate change.

I write with a simple request: as this discussion continues in the world's most developed countries, remember those who live in its poorest regions. Remember that as a result of climate change, this kind of fatal weather event has become commonplace for us while we lack the infrastructure and resources to adequately protect our citizens.

As researchers at Brown University's climate and development lab have shown, climate-related disasters such as droughts, extreme temperatures, floods, and hurricanes have caused an estimated 1.3 million deaths since 1980. Two-thirds of these deaths (over 909,000) occurred in the least developed countries. We are only 12% of the world's population, but we suffer the effects of climate-related disasters more than five times as much as the world as a whole.

Given this reality and your early commitment to leading a science-directed discussion about the changing climate, I was surprised that you only mentioned climate change in your re-election campaign a few times, and not once in your three debates with Mitt Romney. We know that 70% of US citizens now recognise the reality of human-caused climate change. As the world's largest economy, the US has a unique opportunity and responsibility to take bold action on this issue. Indeed, the wellbeing of the citizens of your nation and mine depends on your ability to lead at this critical juncture. It is time to end the climate silence.

Later this month, representatives of the world's nations will meet in Doha, Qatar, for the annual negotiations on the UN climate change treaty. When you were first elected president, your words gave us hope that you would become an international leader on climate change. But you have not lived up to this promise. The framework that you put in place sets the planet on course to warm dangerously, and delays action until 2020 – this will be too late. This year's meeting in Qatar may be our last chance to put forward a new vision and plan to reverse this course. Your legacy, and the future of our children and grandchildren depend on it. We ask you to lead in two ways.

First, join with the European Union, the LDCs and the Alliance of Small Island States in taking on ambitious national commitments to reduce climate pollution. Go beyond the commitments that you made in Copenhagen in 2009. The climate is changing faster than we thought, and we must respond with increased ambition.

Second, provide adequate funding to help the LDCs and other vulnerable nations to adapt to this new climate reality. In 2010, the wealthiest countries directed about $1.5bn to help developing countries adapt to a changing climate. Over the same period, they spent over $400bn subsidising fossil fuel industries. They gave the main contributors to human-caused climate change more than 250 times the support they offered those whom it harms most.

Countries from Gambia and Haiti, to Malawi and Bangladesh need the "predictable and adequate" funding promised in Copenhagen so that they can take simple steps to protect their citizens. This means moving drinking water and irrigation wells away from coasts, where saltwater is intruding into aquifers; it includes developing drought-resistant crops and helping small farmers in fragile, semi-arid regions survive. We have to prepare roads and cities, villages and farms for floods, hurricanes and heat waves. We need to equip people with the weather prediction, early warning systems and emergency response that citizens of the developed countries take for granted.

With 20 years of international climate change negotiations behind us, there is simply no longer time or cause for wealthy countries to continue to stall in taking real action to fulfil the promises they have made. Having the wealthy nations reduce their greenhouse gas emissions steeply is fundamental, but helping the poorest of us cope with its impacts is an immediate necessity.

Mr President, remind the world that the devastation of climate change is shared by all its citizens. Remember that this reality is changeable. Make changing it your legacy.