"...the end of all our exploring will be to arrive where we started and know the place for the first time." - T.S. Eliot

The study of Martian climate and weather is scientifically desirable for comparison with the Earth and the other planets. We seek to understand what the similarities and differences can tell us about the Earth's climate and the physics of any planet's atmosphere. The Earth's climate, of course, is inextricably linked to the evolution and survival of life; the same applies to Mars if it has/had life. The climate of a planet is determined by planetary "constants" such as those listed in the table below, which, in turn, derive from a planet's formation and subsequent evolution. Mars is remarkably similar to the Earth in its rotation rate and axial tilt (see picture above) so both daily and seasonal changes of the Martian atmosphere are fortuitously like the Earth's. Furthermore, both planetary atmospheres are nearly transparent to sunlight so that they are primarily heated by infrared radiation emanating from the surface below. Consequently, many of the principal parameters governing the size of the forces and the nature of the energy exchange in the Martian atmosphere closely resemble the Earth's. As a result, both planets have similar global atmospheric circulation patterns.

An example of how the study of Martian climate has directly impacted thinking about the Earth's climate (and even resulted in political repercussions) is the origin of the "nuclear winter" hypothesis. In the early 1970s, when the Mariner 9 and Viking missions revealed huge dust storms on Mars, this led to computer simulations to determine how such large dust-loadings of the atmosphere would affect the surface temperature on Mars. Such computer simulations have also been applied to Earth's climate, loaded with airborne particles from a large nuclear weapons exchange. It was realized that the Earth's climate would be drastically affected by cooling and that nuclear war was even more of a no-win situation than previously thought.

Moreover, there are numerous examples of meteorological/climate phenomena that apply to both Mars and the Earth. In the winter hemisphere, for example, waves of high and low pressure systems travel eastwards on Mars just as they do on Earth. Terrestrial systems have associated "frontal systems" - sharp boundaries between cold and warm air masses. Fronts also occur on Mars. Terrestrial storms occur in preferred zones, e.g., in the midlatitude oceans of the northern hemisphere. Such "storm zones" also (theoretically) occur in the northern midlatitudes on Mars in low relief regions. On Earth, warm air rises in the tropics, travels poleward at altitude, cools/descends in the subtropics, and returns equatorward near the surface - an overturning called the "Hadley circulation". Computer simulations suggest that such Hadley circulation also occurs on Mars. In the past, geological evidence suggests that the Earth experienced climatic changes explained by alterations in its spin axis inclination and orbit. Likewise, geological evidence also indicates that Mars underwent similar climatic changes, albeit more extreme. Consequently, Mars is a natural laboratory in which we can test our climate theories.

Major meteorological distinctions arise, of course, from the different composition and density of the two atmospheres, the smaller solar heating on Mars, and the non-existence of martian oceans. But nevertheless, the same scientific methodology can still be used to describe each atmosphere. In many ways, the absence of oceans on Mars, which otherwise would have a complex influence on climate, renders Martian meteorology inherently more comprehensible than the Earth's. Beyond the purely scientific goals, Mars climate study provides vital environmental information required to maximize the safety of both robotic and human exploration in the future.

The martian atmosphere itself is the product of the sorting of the planet's initial constituents from the primordial nebula that spawned the solar system 4.6 billion years ago. Therefore, only by fully understanding the present Martian climate can we hope to deduce the climatological, geological, and (possible) biological history of Mars. To this end, our knowledge of the solar system would be enhanced. It is within this broader context that we pursue the study of Martian climate.