What key political decision made by abraham lincoln change the nature of the war in the unions favor?

The Emancipation Proclamation.

It changed the Union's goals and purpose for fighting the war. Their new goal is to free the slaves.

The correct answer is issuing the Emancipation Proclamation.

The Emancipation Proclamation became law on January 1, 1863. The goal of this law was to free slaves within the "rebellious states" (aka the Confederacy). Even though this doesn't technically free slaves since the Confederacy no longer followed the laws put in place by the Union, it turns the tide in the war. This war is no longer about preserving the Union. Rather, the goal of this war is to free slaves and end the institution that helpd spark this Civil War. This allowed thousands of slaves who escaped the Confederacy to join the Union army.

the causes of the dust bowls were severe droughts,   lands became dry and hard, temperature was higher than usual, hot and dry conditions killed crops, high winds. because of those factors, the winds kicked up dry soil and created clouds of dust.