The global distribution of temperature in January is represented through isotherms, which are lines joining places having equal temperature. In general, the effect of latitude is well pronounced as isotherms are generally parallel to the latitude.

In the northern hemisphere, the land surface area is much larger than in the southern hemisphere. Hence, the effects of land mass and ocean currents are well pronounced. In January, isotherms deviate to the north over the ocean and to the south over the continent. The presence of warm ocean currents like Gulf Stream and North Atlantic drift makes the Northern Atlantic Ocean warmer, causing isotherms to bend towards the north. Over land, temperature decreases sharply and isotherms bend towards the south in Europe.

The mean monthly temperature for January is over 27°C in equatorial oceans, over 24°C in the tropics, 2°C to 0°C in the middle latitudes, and -18°C to -48°C in the Eurasian continental interior. In the Siberian plain, the mean January temperature along 60°E longitude is -20°C both at 80°N and 50°N latitudes.

In the southern hemisphere, the effect of the ocean is well pronounced. Here, isotherms are more or less parallel to the latitudes and the variation in temperature is more gradual than in the northern hemisphere. The isotherms of 20°C, 10°C, and 0°C run parallel to 35°S, 45°S, and 60°S latitudes respectively.

Thus, the northern hemisphere shows greater deviation in isotherms due to larger landmass, while the southern hemisphere displays more regular, latitude-parallel isotherms due to oceanic influence.