This can be explained by a few factors: 

People in northern countries often have lighter skin, which is more susceptible to UV damage. Additionally, less frequent sun exposure can lead to riskier behavior, such as overexposure on sunny days or during vacations. 

Despite the cooler climate, UV rays can still be strong in northern regions. Lastly, people in sunnier countries might be more conscious about sun protection, which helps reduce their risk of skin cancer.