Sky lanterns and balloon releases present hazards to animals. While I am sympathetic to those who have lost a loved one, I believe there are many alternative and longer lasting ways to remember them, e.g. tree planting.
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Balloon and lantern releases can have a lasting environmental impact, not only through littering, but some wildlife, livestock, marine life and family pets may mistake them for food, which can lead to death. I believe we collectively have a responsibility to protect our wildlife.