This week on How on Earth Beth interviews two NOAA scientists who study climate change. Joanie Kleypas is a marine ecologist who investigates how rising atmospheric carbon dioxide affects marine ecosystems. She is a self-described optimist who is committed to finding solutions to the “coral reef crisis.” Pieter Tans he has led the Carbon Cycle Greenhouse Gases group at NOAA since 1985. This group has maintained NOAA’s Global Greenhouse Gas Reference Network, producing the most widely used data of atmospheric CO2, CH4, and several other greenhouse gases and supporting measurements.