Final answer:
Large volcanic eruptions decrease global temperatures in the short term due to increased albedo, which reflects sunlight back into space, causing haze-effect cooling. The correct answer is option a.
Step-by-step explanation:
Large volcanic eruptions have the short-term effect of decreasing global temperatures due to the increased albedo of volcanic aerosols. These aerosols, consisting of particles such as sulfur dioxide, can reflect sunlight back into space. This increased reflection of sunlight, known as the haze-effect cooling, acts to lower global temperatures by creating a layer in the atmosphere that blocks some of the sun's energy from reaching the Earth's surface. The 1783 volcanic eruptions in Iceland, which resulted in large volumes of sulfuric oxide emissions and lowered average winter temperatures in Europe and North America, serve as an historical example. Another significant eruption was that of Mount Pinatubo in 1991, which ejected SO₂ aerosols high into the atmosphere, reducing the amount of sunlight reaching the surface and causing a global temperature decrease by 0.4 °C.