Why are January&February usually colder than December in the Northern Hemisphere since the solar angles reach the lowest points in December?
There's a time log in the atmosphere and oceans is why. Water has a high heat capacity, but it takes a long time to heat up AND cool down. Ive gone wading and swimming in The Gulf of Mexico in October and the water temperature is in the 80s degree Fahrenheit range. Water vapor is much more effective greenhouse gas than carbon dioxide.
itscalled thermal lag--terrestrial things such as ocean take time to change
It is known as Thermal Delay Like a time lag due to the Correolis effect Often in Europe, September is a popular month for holidays
There is a delay. Even though insulation in the Northern hemisphere starts to recover just after the solstice, it is still below the annual average and the area covered with snow is still expanding.
In December, there's still some cooling occurring in the oceans that had been heated by the sun. Just like when you turn the oven off, it takes a while to cool...
when you hit the minimum solar angle (and thus lowest solar heating) you do not jump back to normal heat on the very next day. You are still getting less than average heating, so there is still a net loss of heat relative to the average bulk behavior. This ends up appearing as a "lag" in temperatures, because that will not reverse until heat gain starts to approach heat loss and start to actually add more heat than is lost. Temperatures will still fall as long as more heat is lost than gained, even if the amount of loss is smaller than before. Slightly smaller. Eventually, there is a crossover, where decreasing temperature decreases heat loss (radiative heat loss is a function of temperature) to the point where it is less than the heat gain as the sun exposure time increases. That crossover does not happen at the day length minimum. It happens later, when things have gotten even colder.
Global warming affecting the natural stream. This is a very real problem and we as a world, must work together to work on this.
The fact that temperatures dip lowest in December is true and is correctly pointed out in the question. But, people feel colder in Jan or Feb? This is a sensation and is not laboratory data. This question has occurred to many people I know. The answer from SJRTC solar power station weather laboratory would be the rise in humidity in January and early February. Lab data does point out stuff clear, black and white, in broad daylight. @Carol shows that wading and swimming in the Gulf of Mexico does not prove any scientific facts. It's just exercise and fun.