Earth is as close to the Sun today as it will be all year. That doesn't seem right to those of us in the northern hemisphere, where ir's winter and likely cold, but it's all about the tilt of Earth's polar axis. Currently, the northern hemisphere is tilted away from the Sun, so the Sun's energy is spread over a wider area. It's less concentrated, therefore weaker per square measurement, and thus the area the energy covers is colder.
In the southern hemisphere, by contrast, the tilt now is towards the Sun, so when Earth is closest to the Sun, it's summrtime in Sydney.