When is usually the hottest and coldest times of the year usually in the Northern hemisphere?

Question

and how much has this changed you think compared to 50-100 years ago?

besides "global warming", what other reasons could be the cause for the shift, if true you think?

Answer 1

well theres a phenomenon called precession which means every 11 thousand years the seasons move aroungd the calendar by six months ( so that the northern hemisphere would experience summer in january).

This is because earths axial inclination of roughly 23 degrees creates a full circle in the sky every 22 thousand years. This could definately cause global warming (and has).

Also earth orbital eccentricity varies (the amount its orbit deviates from being a circle round the sun) from nealy 0 to 0.05 over a period of 110 thousand years causing differences in the amount of sunlight reaching the earth.

Answer 2

In a majority of locations in the Northern Hemisphere, January is the coldest month, while July is the warmest.  These temperature extremes occur several weeks after the winter and summer solstices because it takes time for the ocean to adjust to seasonal temperature changes (water is resistant to temperature change).

During the previous fifty to one-hundred years, the coldest and warmest times of the year have remained essentially the same.  Global warming is increasing the severity of the temperature changes, but it is not affecting when they occur.  The timing of the temperature changes is controlled almost exclusively by the tilt of the Earth on its axis and the thermal lag imposed by the oceans.  The link in the source box below provides some excellent visuals that illustrate how these controls on temperature change work.