You can do what the Gear Guy does, that's what. And what he wears is this:
Hot weather: If I'm slogging up to Camp Muir on Rainier or otherwise schlepping a load around when it's warm, I'm partial to CoolMax, which has been around for a while but still offers excellent warm-weather performance. Wicks well and dries fast, so much so that it's not out of the question to leave it on as you cool down, and by the time you throw a fleece jacket or shell over the tee, it's dry. L.L. Bean makes a nice one for $20 (www.llbean.com).
Warm weather: Patagonia's Silkweight Capilene is perhaps my favorite base layer for all sorts of conditions. It works well under the same circumstances as the CoolMax, but I tend to wear it when I'm bridging temperature gaps. It's remarkably tough stuff, doesn't pill or fade after repeated washings, and dries super-quickly. Yet it's very soft and, well, silky. $32 in the short-sleeve style (www.patagonia.com).
Cool-to-warm: I lo-o-ve my Icebreaker 190 Tech T ($70; www.icebreaker.com). It's made with super-soft merino wool and is comfortable over a remarkably wide temperature range. It soaks up gobs of sweat so you feel dry, but you don't get chilled after you've stopped working. Slower to dry than synthetics, I concede, but I wear it in all sorts of situations.