The new refrigerant HFO-1234yf is being evaluated for use as a replacement for R-134a in many cooling applictions. It has been proposed to use HFO-1234yf for many AC and refrigeration applications, but we show that is is not a direct replacement for higher performance refrigerants like R-410A for heating and cooling. New refrigerant compositions have been developed and are being evaluated for use in air conditioning and heat pump applications in order to reduce emissions of carbon dioxide and higher GWP gases that can contribute to global climate change. Some of these new composistions are marginally flammable, and are expected to be classified by ASHRAE and ISO as "2L" refrigerants based on low burning velocity and low heats of combustion. This paper presents measured cooling and heating performance results for some of the new candidate refrigerants, and environmental impacts are modeled based on those measured results. Some of the trade-offs impacting envoronmental impact of the developmental refrigerants, including GWP value and energy efficiency performance will be discussed. It is shown the lower GWP fluids do not necessarily give the best environmental performance.