Climate change is without question the environmental hot-button issue of our time. While scientists, politicians and industrialists have long argued whether its causes are naturally occurring or human-induced, the fact is that climate change is happening and the consequences of it are becoming widely apparent and far reaching.

Global temperatures are rising at a record-setting level. The National Oceanic and Atmospheric Administration (NOAA), the American agency that tracks worldwide temperatures, has declared 2015 the hottest year on historical record — going back to 1880, when tracking began on a global scale.

The combination of greenhouse warming and stronger El Niño weather patterns, says NOAA, are producing extreme weather events worldwide — for example, droughts in some areas and flooding in others. Further glaring effects of global warming include melting ice in polar regions that subsequently leads to rising sea levels, as well as longer and more damaging wildfire seasons.

Global sea levels have risen 8 inches since 1880 and are rising at an even faster rate today. Wildfires destroyed more than 9 million acres in the U.S. in 2015 — a loss that has been matched or exceeded during four of the last 10 years.

A variety of far less conspicuous and unexpected effects of climate change are occurring as well. Here are nine of them:

1. Lightning strikes are increasing. Scientists say to expect an increase of 12 percent in lightning strikes for every degree Celsius of temperature gain.

2. Volcanic eruptions will become more frequent. In a related string of events, glaciers melt, the amount of water in oceans increases, global sea level rises — and the weight distribution of the Earth's crust is displaced from land to sea. This shift, volcanologists say, will increase volcanic activity.

3. Warming oceans are killing coral reefs. NOAA oceanographers report that record-high ocean temperatures are causing a massive die-off of the world's coral reefs. The loss could exceed 5 percent in 2016 alone.

4. Allergies will become more severe. Climate change is increasing the spring-summer allergy season, with more pollen in the air for a longer period of time. Some studies suggest the pollen count will double by 2040.

5. A crab invasion will threaten Antarctica. Warming waters along the Antarctic continental slope have invited an influx of shell-crushing king crabs that threatens a varied population of soft-bodied organisms such as starfish, sponges and mollusks, upsetting the continent's delicate ecosystem.

6. Human populations will be displaced. Climate change has already forced the resettlement of a quarter-million people in China's northwest prefecture of Xihaigu where the average temperature has risen by 4 degrees and rainfall has diminished by a third. Also, many low-lying islands in the South Pacific will soon have to be abandoned due to rising seas.

7. Forests in the western U.S. are being decimated. Recent winters have not been cold enough to kill off bark beetles that have destroyed trees over an area larger than the state of Washington.

8. Infectious diseases will worsen. Poor, heavily populated areas of South Asia — Bangladesh in particular — will suffer more from cholera. Cases expected to increase by two to five times.

9. Flowers are blooming in the high Arctic. Things aren't all bad in the face of climate change. Melting snow and ice is making for an earlier Arctic spring and adding more chlorophyll to the soil, prompting flowers such as poppies and saxifrage to grow where they otherwise wouldn't.