The United Nations says agreeing an international climate change deal next month is crucial to fighting global hunger.
The UN says Africa, Asia and Latin America could see a decline of between 20% and 40% in agricultural productivity if temperatures rise more than 2°C.
Government leaders and officials are meeting in Rome for a three-day United Nations summit on food for developing countries.
UN Secretary-General Ban Ki-moon told the summit there could be no food security without climate security.
The number of hungry people in the world topped one billion this year, and the UN says a child dies of malnutrition every six seconds.
Brazil's President, Luiz Inacio Lula da Silva, said hunger was "the most devastating weapon of mass destruction on the planet."