EM radiation comes in a spectrum from radio waves to gamma rays. All types transfer energy in packets called photons. The higher the frequency, the more energy each photon carries. EM radiation can be transmitted, reflected, or absorbed. Ionizing radiation like X-rays and gamma rays can damage DNA through ionization. Non-ionizing radiation like microwaves only heat tissues. The carbon cycle and greenhouse effect influence Earth's climate and temperature. Global warming is likely caused by increased carbon dioxide from human activities. EM radiation is used to transmit both analogue and digital signals for communication technologies.