CLIMATE SCIENCE
This is our first offering in the climate science domain. We do not take sides in the global warming debate. Rather our goal is to provide some of the fundamental numbers and their current explanations to put the debate in perspective.
The understanding of how temperature is regulated on the Earth is an amazing process that requires a vast amount of known scientific theories from physics and chemistry through biology. The sheer range of theory that must be applied is awe inspiring and humbling.
In subsequent offerings, we will explore more data including:
- Major greenhouse gas (water, CO2, and methane) radiation absorbing properties
- Temperature measurements
- CO2 measurements
- Ice, foliage and water coverage
Science has come a long way in understanding this process but we hope to give an appreciation that there is much that is assumed, estimated and perhaps not understood at all.
We hope you will gradually appreciate that climate science is not only about observing melting glaciers or polar ice coverage. Climate science must adhere to the same rigorous standards that has made modern science so successful. In a nutshell, science must create theories that logically and mathematically account for the data.
It is not enough to model each category of data. Scientists demand far more before they believe or accept theoretical explanations that one phenomenon causes another. Specifically, they require that theories - which are to be believed - explain many observations, not just one. This standard accounts for the acceptance of Newton's Laws, Quantum Mechanics and Genetics. These theories explain many things.
The most fundamental process that climate theory must account for is the Earth's radiation budget. Specifically, it must address whether the Earth's atmosphere and surface are accumulating energy from the sun or whether they are able, on the average, to send back to space as much energy as comes in from the Sun.
EARTH RADIATION BUDGET
The radiation budget is a good starting point for understanding the climate problem for the following reason. If more solar energy enters the Earth and its atmosphere than leaves in various forms of radiation, the Earth will heat up. If more radiation leaves than enters, the Earth will cool. For the Earth to remain at a constant temperature, the radiation coming in and going out must balance, must be equal.
This balance does not occur over short periods of time but is thought to occur on the average over many days or months. This balance can be affected by weather changes or ocean current changes to mention a couple of important mechanisms. If these ins and outs could be easily and reliably measured, there would be much less controversy about whether there is an excess of of inbound radiative energy but this is not the case.
The numbers presented here assume that the Earth is not heating or cooling. That is they are presented in balance. This does not mean that the Earth is not cooling or heating as a whole in reality. Rather, the numbers were developed to gain an understanding of the relative importance of all the various components. The numbers provide a foundation for scientists to refine measurements to better understand how these processes may affect the heating or cooling of the planet.
Some may say, "but glaciers are melting" or "antarctic ice sheets are expanding" or their local climate has changed. All these observations may be true where they are true but these observations do not necessarily say that the planet as a whole is gaining or losing energy from the sun. That's the big question.
The radiation budget numbers presented on this site are for the whole planet averaged over time for weather changes and orbital motion. They are based on measurements but each component is not actually measured. Some are inferred.
Measuring Temperature
The other way to get a handle on the radiation balance is of course to measure the effects of the radiation process - that is measure temperatures both current and past. But this is not without challenges either, principally because the Earth is a very inhomogeneous place.
In other words, the temperature varies from place to place over the Earth's surface and within its atmosphere. Any concept of an average temperature will depend on how the temperatures that are measured are averaged together and this average depends on assumptions not measured. Temperatures cannot be measured everywhere - they are sampled at a finite number of particular locations.
The further one looks into the past, the more sparse the recorded temperature record becomes. Directly recorded temperature records are at most several hundreds of years old which is miniscule in comparison to climate time scales of thousands or millions of years. Past temperatures must be inferred by making measurements such as dissolved gases in ice cores. All of these measurements depend on assumptions of how, for example, ice was laid down and whether it has moved and how the gas was trapped. It is difficult to ascertain how good such assumptions are.
In summary, what we are trying to relay is that observational measures of climate are challenging and subject to significant error even for measurements made today with the most sophisticated devices. Historical measurements have significantly more error which may not even be quantifiable.
Theoretical Challenges
This is not the only challenge faced by climate scientists. There is an enormous theoretical challenge. They are trying to tie together diverse sciences including quantum mechanical theories of radiation, thermodynamics, chemistry, biochemistry, fluid dynamics, biology and transport theory. In order to incorporate all important scientific theory, the models become so complex, that it is difficult to use them to make predictions. Scientists therefore have to make approximations and assumptions and, as stated above, use imperfect data as a starting point. In other words, scientists must balance using models that use science they are certain of but which the math is very hard to solve against models where the math is easier but whose theoretical assumptions are less certain. Reasonable scientists may disagree where to draw this line.
Unexplained Science
There is one last point, often overlooked in this incredibly challenging endeavor to understand our climate. There may be fundamental physics and chemistry that is not yet understood or even overlooked and therefore not yet included in the models. For example, scientists are still debating such important phenomena as how clouds form, how storms evolve and the origin of lightning. These processes are likely to be intimately involved in the Earth's thermal regulation system.
UNDERSTANDING THE RADIATION BALANCE
Climate scientists trying to quantify all the energy entering and leaving the Earth assume that for the Earth not to cool or heat, (1) the energy entering from the sun and leaving through radiation to space must be equal and (2) the energy cross from above the Earth - atmosphere boundary must be equal to the energy crossing from below. They measure what they can and use these assumptions to quantify what is not easily measured.
Before explaining these two balances, we will discuss all of the relevant processes that move energy past these boundaries, some involve electromagnetic radiation, and some involve transport of heat and material.
What is Measured and What is Estimated.
It is difficult to categorize each of the numbers presented as either measured or inferred. In fact, these numbers are some of both. Perhaps the best measurements are for the energy entering and leaving the atmosphere. When scientists estimate the other numbers, they make sure that their models always are consistent with the measured values of incoming and outgoing radiation. Even these numbers are not precise enough to know whether there is a radiation balance.
An example of a number that is part measured and part inferred is the number for evaporative transfer of energy from the Earth to the atmosphere. This is inferred from the measured amount of global rainfall and snow - an imperfect number. The assumption is that the amount of evaporation is the same as the amount of precipitation. It is further estimated from the amount of heat given up when water vapor condenses to ice or liquid water - a number which depends on the the local temperature and pressure where the precipitation occurs - which is not likely measured.
Incoming Solar Energy (Table 1)
Sunlight that enters the atmosphere is mainly in the form of visible light with wavelengths from about 0.25 to beyond 2.0 microns (millionths of a meter) peaking at 0.5 microns (green light). The spectrum falls to about 10% of its peak intensity at about 1.5 microns. This light undergoes four (4) processes: (1) reflection by the atmosphere and clouds back out to space, (2) reflection by the Earth's surface including the oceans back out to space, (3) absorption by the atmosphere causing heating, and (4) absorption by the Earth's surface, including the oceans, causing heating.
Energy Leaving the Earth's Surface
Solar energy entering the surface of the Earth heats it. Energy leaves leaves the Earth's surface in four ways which are explained below: (1) reflection of visible solar radiation, (2) emission of thermal infrared radiation, (3) conduction of heat from the surface to the atmosphere, and (4) evaporation of water.
Absorption of Solar Radiation. Everybody has experienced the effects of the sun's warming. Through a complex of physical interactions between the sun's radiation and matter comprising the Earth's surface, the sun's energy is transferred to matter, warming it.
Thermal Radiation. A basic principle of physics is that matter radiates with a spectrum that is characterized by its temperature. This is why the Earth's surface radiates infrared radiation (a form of electromagnetic radiation invisible to the human eye), also called thermal radiation. The sun also obeys this principle, radiating light characteristic of its temperature of about 6000 degrees centigrade.
Heat Conduction. When a hot material comes in contact with a colder material, heat flows from the hotter to the colder, the hotter material cools and the cooler material warms. The same happens between the Earth and its atmosphere.
Evaporation. Water evaporates at the temperatures prevailing on the Earth. This process occurs all over the Earth with evaporated water carrying energy from the Earth's surface to the atmosphere.
Clear Atmosphere
As in the case of the Earth, the atmosphere is interacting with two major categories of radiation: (1) the sun's radiation (visible and ultraviolet) and (2) infrared radiation. We have already stated that it absorbs and reflects sunlight. The atmosphere also (1) interacts with the infrared radiation leaving the Earth's surface and (2) generates its own thermal radiation.
Its absorption of the Earth's infrared radiation produces the so-called Greenhouse Effect. The absorbers that play the largest role are water and carbon dioxide (CO2) with water playing the largest role. When these molecules absorb infrared radiation, they in turn re-emit it, with some being returned to the Earth where it is absorbed again causing heating (Greenhouse effect), some is absorbed at another place in the atmosphere and some escapes to space.
Clouded Atmosphere
All the processes of the clear atmosphere are present in cloudy conditions but they are complicated by additional processes. This includes reflection and absorption from clouds of inbound solar radiation, reflection and absorption of the Earth's infrared radiation and the clouds' own thermal radiation.
Water vapor that carried energy away from the Earth heats the atmosphere when it condenses to liquid water or ice, thus completing the transfer of energy that began with evaporation. The complex processes whereby water vapor is eventually returned to the Earth in the form of precipitation liberates substantial thermal energy (some even think radiative energy) and is intimately involved in storms.
Top of Atmosphere (Table 2)
The incoming solar radiation is balanced by reflections from the atmosphere, its clouds, the Earth's surface plus all the sources of infrared radiation coming from the Earth, the atmosphere and the clouds.
Earth - Atmosphere Boundary - Bottom of Atmosphere (Table 3)
The infrared radiation emitted by the atmosphere including clouds plus solar energy passing through the atmosphere is balanced by the infrared radiation emitted from the Earth, the solar energy reflected by the Earth, heated conducted from the Earth to the atmosphere and energy transfered by water evaporation.
