Unfortunately, there are those who think that the Earth's climate was stable, until we came along and messed it up with our burning of fossil fuels. We may be messing it up to some extent, but the global climate was never some constant state. There never was a perfect climate that we need to protect and maintain.

There are many reasons why the Earth's climate is always changing. 

1.    The Earth is not always the same distance from our primary source of heat, the sun, and its orbit is elliptical. Because of this, the Earth is closer to the sun at some times of the year and farther away at other times. To complicate this picture, the Earth's orbit is constantly changing. Furthermore, the entire solar system orbits around the gravitational center of the galaxy. This motion carries us through regions of space with different quantities of interstellar gases and particulates which also affects how much and what kind of solar radiation reaches the Earth.

2.    The tilt of the Earth's axis is not always the same and therefore, seasonal variations differ as this tilt changes.

3.    The Earth wobbles as it spins, once every 26,000 years, and this causes the northern and southern hemispheres to be more directly facing the sun at different times in it's orbit around the sun. At the present, it is winter in the northern hemisphere when we are closest to the sun and farthest from the sun in the northern hemisphere summer.

4.    The sun is a variable star. Its output of solar energy varies over time and in cycles that are fairly well understood.

5.    The Earth itself is a source of heat that enters the oceans and the atmosphere. This heat is from nuclear fission reactions that occur within the planet where radioactive substances undergo their predictable decay. The heat released is significant enough to melt rock. Over time, this heat is released through fissures, volcanoes, and through the Earth's crust in general.

6.    The atmosphere is constantly changing in composition. Some components of the atmosphere absorb heat that is radiated from the surface. Other components of the atmosphere block heat from reaching the surface. There is circulation in the atmosphere which is influenced by oceans and landforms as well as by the sun and seasons.

7.    More than three-fourths of the Earth's surface is water. As water heats, it releases dissolved gasses into the atmosphere, as it cools, it absorbs gases. Most of the dissolved gasses in the oceans originate from within the Earth's crust under the oceans. The oceans also absorb gases from the atmosphere. Precipitation systems have a significant influence on the transport of gases and heat energy between the oceans and the atmosphere.

8.    The oceans' currents are constantly flowing and changing. There are well understood annual, multidecadal, and other long-term cycles of ocean current variations. There are cold and warm currents. Ocean currents have a profound influence on local climates over all of the land masses of the Earth.

9.    The continents and the Earth's crust are constantly moving, up and down, back and forth. The crust exists in sections called plates which slide past each other, collide, move apart. The crust generally rises after glaciers melt and pushes down into the mantle when they accumulate. Both land elevations, the distance from the center of the Earth, and sea levels are constantly changing all over the Earth. Changes in sea level should be described relative to some frame of reference. Not all oceans are at the same level or changing in the same direction. The Atlantic Ocean is enlarging, the Pacific is getting smaller.

10. Human activity changes the surface of the Earth and also the composition of the atmosphere. Other living creatures of all kinds do this as well. Virtually all of the oxygen in our atmosphere came from green plants through photosynthesis. Until there were green plants, there was no significant amount of oxygen and there were no air-breathing animals either.

The Earth is currently in an interglacial within an ice age. Yes, we are in an ice age, perhaps the fourth such age since the Earth was formed. The planet has been generally warming for about 18,000 years. The last glacial period ended about 12,000 years ago and sea level has been rising ever since. When Columbus discovered the indigenous peoples of the Caribbean in 1492, sea level was several feet lower than today. The first human activity that had a measurable influence on climate was agriculture which began to affect local climate about 8,000 years ago.

Now, the question remains, how much influence does human activity have on our climate? That is the great debate. Some anthropogenic influences cause the atmosphere to warm while others cause it to cool. Unfortunately, our climate models are not sufficiently sophisticated to answer this question, yet. It is even possible that human activity causing warming might delay our next global cooling period. Wouldn't that be ironic? If you get to choose whether you want to get warmer or cooler, pick warmer! Cooler is a real killer!

The climate is going to continue to change, no matter what we humans do, and it would be changing, even if we did not inhabit this planet. We need to focus our attention on adapting as well as protecting.