Some people say that the extinction of plants and animals is the biggest environmental threat we face today. I agree with this matter but I think the biggest problem is climate change.
The loss of some plants and animals will break the food chain and cause problems. For example, when predatory animals like tigers at the top of the pyramid disappear, it will lead to an uncontrollable increase in the number of herbivores. The loss can be caused by nature or human activity but based on my opinion, human activity is the biggest cause.
On the other hand, climate change is caused by human activity too and it's an even bigger challenge. Because of the pollution and the green house gas effect, global temperatures are rising then the polar ice is melting. It causes sea levels increase. The world are already facing the risk of getting submerged in the oceans, especially coastal cities. Climate change also leads to more frequent occurrences of droughts and flooding. This affects food production and health problems for humans and animals. If the temperature continues to rise at this pace, the planet may become inhabitable in the future.
In conclusion, the extinction of wildlife and the loss of biodiversity are big issues. However, climate change and the associated problems are even bigger challenges as they can threaten the existence of life on the planet. 
 Some
  people
 say that the extinction of plants and  
animals
 is the biggest environmental threat we face  
today
. I  
agree
 with this matter  
but
 I  
think
 the biggest  
problem
 is  
climate
  change
.
The loss of  
some
 plants and  
animals
 will break the food chain and cause  
problems
.  
For example
, when predatory  
animals
 like tigers at the top of the pyramid disappear, it will lead to an uncontrollable increase in the number of herbivores. The loss can  
be caused
 by nature or  
human
 activity  
but
 based on my opinion,  
human
 activity is the biggest cause. 
On the other hand
,  
climate
  change
  is caused
 by  
human
 activity too and it's an even bigger challenge.  
Because
 of the pollution and the green  
house
 gas effect, global temperatures are rising then the polar ice is melting. It causes sea levels increase. The world are already facing the  
risk
 of getting submerged in the oceans,  
especially
 coastal cities.  
Climate
  change
  also
 leads to more frequent occurrences of droughts and flooding. This affects food production and health  
problems
 for  
humans
 and  
animals
. If the temperature continues to rise at this pace, the planet may become inhabitable in the future. 
In conclusion
, the extinction of wildlife and the loss of biodiversity are  
big
 issues.  
However
,  
climate
  change
 and the associated  
problems
 are even bigger challenges as they can threaten the existence of life on the planet.