Scientists have adopted basic rules of management, such as: "You can't manage what you can't measure." This is a truism in climate science. In order to understand where our climate is headed, we need to know where it has been in the past, and where it is now.

Understanding the state of the climate is an immense engineering challenge. Think of trying to measure the energy of the oceans, or the chemistry of the Earth's waters. How about temperatures or chemistry of the atmosphere? What about the extent of ice (including both area and thickness)? How about sea level?

What is particularly challenging is that these quantities have to be measured all over the globe, not just in a few locations. Furthermore, they have to be measured continuously for decades. Some properties have been measured for very long periods of time, but this is no guarantee these measurements are accurate. Techniques and technologies change over the years.

Take, for instance, ocean temperatures. Measurements from as far back as the 1700s were recorded, but they were sparse in coverage. Later, more systematic measurements of ocean waters were made with canvas buckets, then insulated buckets, and then using more and more advanced systems until today, when approximately 3,000 automated floats continuously record and transmit ocean temperatures. Splicing together these records from differing technologies is challenging and often gives misinterpretations of long-term trends.

International Argo Program – Photograph of an Argo float used to measure ocean temperature and salinity

In the late 1970s, satellites began to take an ever increasing role in earth observations. Satellites have the ability to take thousands of measurements each day and cover the entire globe. They are, however, not without their own weaknesses. Satellites are only in place for short periods of time, typically a few years. This means they have to be replaced continually. Matching up data from different satellites with overlapping periods is challenging.

Satellites may also have biases that must be corrected. In the 1990s, two scientists thought they had shown that the lower part of the atmosphere was cooling – in contrast to expected global warming effects. It was later shown (here, here, here, and here) that the two scientists had made serious errors in their analyses of the satellite data. Now, all satellite data is in agreement – the Earth is warming just as we expected.

So what is the future of Earth observing systems? Will they survive in this era of budget cuts? The answer is, I don't know. But I can relate some key systems that we should look out for. One is the Tropical Atmosphere Ocean (TAO) array which consists of 55 oceanic moorings that

measure ocean temperatures and interactions between the ocean and atmosphere in the Pacific. According to NOAA scientist Dr. Michael McPhaden, the moorings' health is rapidly deteriorating – 17 of the moorings are off-line and the amount of recorded data is at about 50%. In his words, this system is now "on life support". Consequently, planning for and adapting to natural disasters will be compromised.

NOAA photograph of a TAO mooring

Another critical set of instruments is the JASON satellite series. According to Dr. Joshua Willis of the Jet Propulsion Laboratory, this series comprises one of the most important observation systems we have. Those satellites measure, among other things, sea level rise. Accurate knowledge of sea level rise helps scientists understand how much extra energy the Earth is absorbing from greenhouse gases.

NASA illustration of a JASON satellite

Another critical set of measurements deals with ocean chemistry. These measurements tell us how fast the ocean is absorbing excess carbon dioxide from the atmosphere. NOAA has a measurement program which it hopes will provide high-quality information about ocean acidification – another "greenhouse gas problem" that threatens certain types of sea life.

All of these programs, and many others I haven't mentioned, require adequate funding for equipment and personnel. Presently, many systems – in particular satellite platforms – are headed for declines in coverage. This means we will be operating blindly, in an information deficit. If we are to make good decisions about how to react to greenhouse gas increases, we need good information. When the economic costs of climate change are compared with the very modest costs of measurement, it seems that maintaining a robust measurement capacity is a no-brainer.