How come it’s coldest when we are closest to the sun and warmest when we are furthest away?

The average global atmospheric temperature is warmest during the northern hemisphere summer because most of the earth's landmass is in the northern hemisphere. Land warms faster than water, so the atmosphere is warmed more.

I haven't looked it up and thus have no source but I have an educated guess.

The Northern Hemisphere had a much higher land to ocean ratio than the Southern Hemisphere. As you know, the oceans act as a temperature moderator. So the summer to winter temperature swings in the Northern Hemisphere are greater and likely drive the global average into the trend that you indicated.

I'll even go out on a limb and say that when the eccentricity of the Earth's orbit changes and January is no longer the month when Earth is closest to the Sun, then the global average will vary even more than it does now and this might be the trigger for an ice age (i.e Milankovitch cycle for orbit eccentricity).

That's an average. Cooler temperatures in Nov - March are only for the Northern Hemisphere. The Southern Hemisphere is the opposite, with the warmest temperatures occurring at perihelion and the coolest at aphelion.

The Earth's orbit is near-circular, the difference in distance is tiny compared to the average distance from the Sun. Remember also that climate is complicated - ocean currents carry heat energy around and have a massive effect on climate. The energy received from the Sun is absorbed differently by different types of land and by water, and moved around a lot, so it is not a simple case of energy received immediately translating to a change in temperature. There can be a delay of weeks or months.

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Edit: yes, I realised that after submitting my answer, so I already edited it to correct myself.

Edit 2: I haven't misunderstood anything, I simply made my answer quite simple and straightforward - I saw no need to overcomplicate things.

Apology accepted :) :) :)

Of course, you are talking of the planet as a whole; RR seems to have slightly misunderstood the question.

The answer would have to be due to the uneven distribution of land between the hemispheres. Land masses show a greater annual temperature variation than oceans so, when the northern hemisphere has its summer season, the greater land mass in that hemisphere causes average GLOBAL temperature to rise. In the NH winter, the opposite happens.

The Earth does get more sun in NH winter, that's true; the orbit is changing though, and there will come a time when the two effects are in phase and we will get more extreme NH summers and winters.

This is due to precession and is one of the Milankovitch cycles. From memory, this cycle takes around 26000 years. In combination, the Milankovitch cycles are responsible for the ice ages and interglacials that dominate our climate over periods of 100 000 years or so.

http://en.wikipedia.org/wiki/Milankovitch_cycles

Edit: I see RR has spotted and corrected his/her error in the time I took to type. Apologies to RR.

Edit: Dave, your follow up question seems to be incomplete. It looks interesting though, hopefully you can either finish it here or put it as a separate question. Meanwhile, here's a star.

Later: That's an interesting question and I have no idea why that should be so. If I was to guess, it would be that heat is exchanged at the air/ocean boundary. Heat flows from warmer to cooler so if (in NH summer), more warm air from the land comes into contact with cooler water, this will raise the average SST.

In NH winter, the reverse would happen because the air from the land is now cooler than the SST. The average SST probably doesn't change that much between summer and winter.

But, as I said, that's just a guess. It could be completely wrong!

Aside from those already mentioned dealing with more land in the northern hemisphere I think I saw it listed before that the ocean has the ability to store heat energy for a longer time period which is one of the reasons why the warmest part of the day isn't when the Sun is directly over head but is instead a few hours afterward.

Maybe it's a bit like how seawater seems to get warmer well in to the night and then becomes quite cold at around ten a.m before startign to warm up again.

It takes some time to absorb the heat and some time to dissipate it.

The numbers given are a global means. The distinction between land and water are of little consequence considering temperature moderators... regional or hemispheric would be the exception. The largest being water the second being the atmosphere which interacts with water: http://science.nasa.gov/earth-science/oceanography...

The rate, duration and forcing of energy exchange between each moderator is extremely complex. Though some will tell you otherwise: http://en.wikipedia.org/wiki/Thermal_flywheel_effe...

All those other theories are quite interesting and may have some merit, but the PRIMARY reason those of us in the Northern hemisphere are warmer when we are further away is because the angle the sun hits us is more direct in the summer more than offsetting the very small difference in distance. Conversely, those in the Southern hemisphere are warmer when they're closer because they get more direct sunlight then.