Elfatih Eltahir

"Climate models are numerical models. They are numerical solutions of a set of partial differential equations —coupled partial differential equations.

"The way I describe them to my students is, you could think of seven principles described with seven equations in seven variables. And the principles are conservation of water mass, air mass, conservation of energy, conservation of momentum in three directions, and the state equation for air, the ideal gas law. So those are seven principles. 

"You describe them with seven equations. And you solve for seven variables, which are pressure, temperature, humidity, density and wind in three directions. So, you have seven equations, seven variables. You solve them on a sphere for the atmosphere. You solve a similar set of equations for the ocean, you couple them.

"When you come then to describe impacts on things like disease and agriculture and others, you have to develop other models that are tailored to describe those phenomena in accurate ways. 

"Always you develop the models and you test them against the past climate. So, we have a lot of data for the last number of years —at least 30 or more years —and we test the models against those, we calibrate them for those conditions that have been observed before we use them to project the future. 

"And this process is an ongoing process, we are always coming up —not just my group —but globally scientists are coming up with better models. They are better representations improving on their accuracy, and they’re reducing the uncertainty. And that’s an ongoing process that happened in the past and will continue to happen in the future."