The first step in dealing with climate change is to understand its drivers and mechanisms and use that knowledge to examine the likely consequences of human actions. Those mechanisms are surpassingly complex and operate throughout the atmosphere, oceans, and ecosystem. It's not enough simply to monitor global surface temperatures. That tells us it's getting warmer but reveals little about the causes of that warming or its future course. For starters we must document the evolving thermal structure of the global atmosphere from the surface to the upper stratosphere. Until now, however, there have been no instruments able to achieve the required measurement accuracy and long-term stability above the surface.